This paper summarizes the special interest group discussion about slides sets for use by Astronom... more This paper summarizes the special interest group discussion about slides sets for use by Astronomy 101 instructors. The NASA Science Mission Directorate Astrophysics Education and Public Outreach Forum is coordinating the development of a pilot series of slide sets to help Astronomy 101 instructors incorporate new discoveries in their classrooms. The “Astro 101 slide sets” are presentations of 5–7 slides on a new development or discovery from a NASA Astrophysics mission relevant to topics in introductory astronomy courses. We intend for these slide sets to help Astronomy 101 instructors include new developments (discoveries not yet in their textbooks) into the broader context of the course. With their modular design and non-technical language, the slide sets may also serve audiences beyond Astronomy 101 instruction and are adaptable to different needs. An example on exoplanets was highlighted in this session. In this paper, we outline the community feedback, which falls into the bro...
Recently, X-ray Fluorescence Holography (XFH) (M. Tegze and G. Faigel, Nature 380 (1996) 49) and ... more Recently, X-ray Fluorescence Holography (XFH) (M. Tegze and G. Faigel, Nature 380 (1996) 49) and Multiple Energy Xray Holography (MEXH) (T. Gog et al., Phys. Rev. Lett. 76 (1996) 3132) have been demonstrated as structural probes of short-range atomic order, by which three-dimensional images of the atoms surrounding a species-specific fluorescence site can be obtained by numerical reconstruction of holographic fluorescent diffraction intensities. We relate these two experimental techniques of obtaining such diffraction intensities, and theoretically demonstrate the atomic images that may be obtained from certain short-range-ordered structures that can be fruitfully studied by XFH and MEXH.
Photoelectron diffraction data can, in principle, be regarded as enabling the experimental record... more Photoelectron diffraction data can, in principle, be regarded as enabling the experimental recording of electron diffraction phases ͑relative to a direct reference wave͒, as well as intensities, thus also permitting the holographic reconstruction of atomic positions. Such holographic photoelectron diffraction patterns have been measured for surface and bulk core-level-shifted W 4 f photoemission from W͑110͒, yielding a data set of unprecedented size and quality. To test the role of experimental uncertainties and of multiple-scattering effects, we have also performed corresponding theoretical calculations at the single-and multiple-scattering levels. The surface and bulk holograms so obtained have been analyzed so as to provide the first parallel comparison of the three-dimensional atomic images that can be directly obtained via the five principal reconstruction algorithms proposed to date. The advantages and disadvantages of each of these methods are discussed. The prospects and limitations of atomic photoelectron holography as an ab initio technique for determining local-surface structures are also explored. ͓S0163-1829͑99͒08207-7͔
Multi-energy x-ray holography data from a natural hematite (Fe_2O_3) crystal are interpreted and ... more Multi-energy x-ray holography data from a natural hematite (Fe_2O_3) crystal are interpreted and utilized to directly image the immediate atomic Fe environment by use of a holographic Fourier transform of the diffraction intensity data set in reciprocal space. We compare these experimental images with the images reconstructed from a theoretically equivalent Fe cluster. We discuss the removal of real-twin image overlaps due to the multiple energy range of the holographic data, and the effect of the polarization of the incident monochromatic beam in reducing the effective size of the imagable cluster. We will also discuss the likely future prospects for this new method.
Len, Patrick ; Thevuthasan, Suntharampillai ; Fadley, Charles S. ; Van Hove, Michel A. ; Denlinge... more Len, Patrick ; Thevuthasan, Suntharampillai ; Fadley, Charles S. ; Van Hove, Michel A. ; Denlinger, Jonathan D. ; Tonner, Brian P. ; Rotenberg, Eli ; Kevan, Stephen D. ; Gog, T. ; Materlik, G.
Two limiting-case algorithms have previously been proposed for holographically imaging atoms near... more Two limiting-case algorithms have previously been proposed for holographically imaging atoms near surfaces using photoe!cctron diffraction data and other diffraction data associated with electron emission: (i) a phased sum of Fourier transforms of scanned-angle data taken at several energies from Barton, (ii) and a phased sum of Fourier transforms of scanned-energy data taken along several directions due to Tong et al. We first point out that both methods are equivalent three-dimensional transforms in the wave vector k of the emitted electron, differing only in the way they sample k-space. A continuum of different sampling densities in the direction and magnitude of k exists in such holography, spanning the two limits previously discussed. An additional variant on these methods involves using only a small cone of data in k-space for each transform. Using model diffraction calculations for localized electron emission (e.g., core photoelectron emission) from Cu(001) clusters, we have explored the full range of k-space sampling possible, and find that optimum image quality is expected for choices intermediate between the extreme limits of scanned-angle or scanned-energy. General rules for optimizing image quality for a given data-set range are also discussed, and used to evaluate the sampling choices made in some prior experimental studies.
The current status of photoelectron-diffraction studies of surface structures is briefly reviewed... more The current status of photoelectron-diffraction studies of surface structures is briefly reviewed, and several recent developments and proposals for future areas of application are then discussed. The application of full-solid-angle diffraction data, together with simultaneous characterization by low-energy electron-diffraction and scanning-tunneling microscopy, to epitaxial growth is considered. Several new avenues that are being opened up by third-generation synchrotron-radiation sources are also considered. These include photoelectron diffraction from surface and interface atoms, the possibility of time-resolved measurements, and circular dichroism in photoelectron angular distributions. The addition of spin to the photoelectron-diffraction measurement is also considered, and can be achieved either through core-level multiplet splittings or by circular-polarized excitation of spin–orbit-split levels. This last development should make it possible to study short-range magnetic orde...
Journal of Electron Spectroscopy and Related Phenomena, 1995
ABSTRACT Images of near-surface atoms can be obtained from photoelectron diffraction data by vari... more ABSTRACT Images of near-surface atoms can be obtained from photoelectron diffraction data by various imaging algorithms, the basic method being: (a) a Fourier transform over k-space involving a path-length difference phase factor. We will also discuss two recently proposed direct methods that compensate for the non-optical atomic scattering of photoelectrons: (b) a Fourier transform of small k-space cones centered on the approximately optical scattering regions of a photoelectron diffraction data set; and (c), a truly quantum mechanical Fourier transform that accounts for the non-optical propagation and atomic scattering of the photoelectrons in the first Born approximation. Atomic images produced by these three methods are compared for photoelectron diffraction patterns calculated from a single scattering Ni trimer, and a large multiple scattering Ni bulk cluster. All three methods are found to comparably resolve backscattering atomic images, while poorly resolving forward and side scattering atomic images.
... From that point through the rest of the semester, student interaction during review questions... more ... From that point through the rest of the semester, student interaction during review questions was much more animated, with a marked increase in discussion among students and within small groups. ...Astronomy 10 is a one-semester survey course at Cuesta College. ...
In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT)... more In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT) system, which has been jointly developed between the University of California Davis Cancer Center and Varian Associates. BSRT is a description of an emerging radiation oncology procedure, where simulation, CT scan, treatment planning, and radiation treatment are synchronized with voluntary breath‐hold, forced breath‐hold, or breathing gating. The BSRT system consists of a breathing monitoring system (BMOS) and a linear accelerator gating hardware and software package. Two methods, a video camera‐based method and the use of wraparound inductive plethysmography (RespiTrace), generate the BMOS signals. The BMOS signals and the synchronized fluoroscopic images are simultaneously recorded in the simulation room and are later analyzed to define the ideal treatment point (ITP) where organ motion is stationary. The BMOS signals at ITP can be used to gate a CT scanner or a linear accelerator to ...
International Journal of Radiation Oncology*Biology*Physics, 1999
Selective gene expression in response to the tumor-specific microenvironment may provide new aven... more Selective gene expression in response to the tumor-specific microenvironment may provide new avenues for cancer treatment. In this study, we have established a hypoxia inducible vector system for specific production of therapeutic genes in tumors and have assessed its in vitro and in viva efficacy.
ABSTRACT A complete angle- and energy-dependent photoelectron diffraction data set has been measu... more ABSTRACT A complete angle- and energy-dependent photoelectron diffraction data set has been measured for bulk and surface 4f core-level emission from clean W(110). This data set, the largest for a surface core-level to date, consists of uniform sampling over a large k-space range encompassing nearly 2pi emission angles with 0.1 inverse Angstrom momentum steps. Volume representations of the data visually highlight the transition from multiple- scattering to back-scattering energy regimes. These high density data sets, taken at the high-brightness undulator soft x-ray beamline 7.0 at the Advanced Light Source, provide a stringent test for electron-scattering simulations and for direct holographic inversion algorithms. Most photoelectron holography experiments to date have used an approximation to a three-dimensional Fourier integral due to coarse sampling in either angles or energy. Comparison will be made of experiment to single- and multiple-scattering theories; and a comparison of four different holographic inversion algorithms will be presented.
This paper summarizes the special interest group discussion about slides sets for use by Astronom... more This paper summarizes the special interest group discussion about slides sets for use by Astronomy 101 instructors. The NASA Science Mission Directorate Astrophysics Education and Public Outreach Forum is coordinating the development of a pilot series of slide sets to help Astronomy 101 instructors incorporate new discoveries in their classrooms. The “Astro 101 slide sets” are presentations of 5–7 slides on a new development or discovery from a NASA Astrophysics mission relevant to topics in introductory astronomy courses. We intend for these slide sets to help Astronomy 101 instructors include new developments (discoveries not yet in their textbooks) into the broader context of the course. With their modular design and non-technical language, the slide sets may also serve audiences beyond Astronomy 101 instruction and are adaptable to different needs. An example on exoplanets was highlighted in this session. In this paper, we outline the community feedback, which falls into the bro...
Recently, X-ray Fluorescence Holography (XFH) (M. Tegze and G. Faigel, Nature 380 (1996) 49) and ... more Recently, X-ray Fluorescence Holography (XFH) (M. Tegze and G. Faigel, Nature 380 (1996) 49) and Multiple Energy Xray Holography (MEXH) (T. Gog et al., Phys. Rev. Lett. 76 (1996) 3132) have been demonstrated as structural probes of short-range atomic order, by which three-dimensional images of the atoms surrounding a species-specific fluorescence site can be obtained by numerical reconstruction of holographic fluorescent diffraction intensities. We relate these two experimental techniques of obtaining such diffraction intensities, and theoretically demonstrate the atomic images that may be obtained from certain short-range-ordered structures that can be fruitfully studied by XFH and MEXH.
Photoelectron diffraction data can, in principle, be regarded as enabling the experimental record... more Photoelectron diffraction data can, in principle, be regarded as enabling the experimental recording of electron diffraction phases ͑relative to a direct reference wave͒, as well as intensities, thus also permitting the holographic reconstruction of atomic positions. Such holographic photoelectron diffraction patterns have been measured for surface and bulk core-level-shifted W 4 f photoemission from W͑110͒, yielding a data set of unprecedented size and quality. To test the role of experimental uncertainties and of multiple-scattering effects, we have also performed corresponding theoretical calculations at the single-and multiple-scattering levels. The surface and bulk holograms so obtained have been analyzed so as to provide the first parallel comparison of the three-dimensional atomic images that can be directly obtained via the five principal reconstruction algorithms proposed to date. The advantages and disadvantages of each of these methods are discussed. The prospects and limitations of atomic photoelectron holography as an ab initio technique for determining local-surface structures are also explored. ͓S0163-1829͑99͒08207-7͔
Multi-energy x-ray holography data from a natural hematite (Fe_2O_3) crystal are interpreted and ... more Multi-energy x-ray holography data from a natural hematite (Fe_2O_3) crystal are interpreted and utilized to directly image the immediate atomic Fe environment by use of a holographic Fourier transform of the diffraction intensity data set in reciprocal space. We compare these experimental images with the images reconstructed from a theoretically equivalent Fe cluster. We discuss the removal of real-twin image overlaps due to the multiple energy range of the holographic data, and the effect of the polarization of the incident monochromatic beam in reducing the effective size of the imagable cluster. We will also discuss the likely future prospects for this new method.
Len, Patrick ; Thevuthasan, Suntharampillai ; Fadley, Charles S. ; Van Hove, Michel A. ; Denlinge... more Len, Patrick ; Thevuthasan, Suntharampillai ; Fadley, Charles S. ; Van Hove, Michel A. ; Denlinger, Jonathan D. ; Tonner, Brian P. ; Rotenberg, Eli ; Kevan, Stephen D. ; Gog, T. ; Materlik, G.
Two limiting-case algorithms have previously been proposed for holographically imaging atoms near... more Two limiting-case algorithms have previously been proposed for holographically imaging atoms near surfaces using photoe!cctron diffraction data and other diffraction data associated with electron emission: (i) a phased sum of Fourier transforms of scanned-angle data taken at several energies from Barton, (ii) and a phased sum of Fourier transforms of scanned-energy data taken along several directions due to Tong et al. We first point out that both methods are equivalent three-dimensional transforms in the wave vector k of the emitted electron, differing only in the way they sample k-space. A continuum of different sampling densities in the direction and magnitude of k exists in such holography, spanning the two limits previously discussed. An additional variant on these methods involves using only a small cone of data in k-space for each transform. Using model diffraction calculations for localized electron emission (e.g., core photoelectron emission) from Cu(001) clusters, we have explored the full range of k-space sampling possible, and find that optimum image quality is expected for choices intermediate between the extreme limits of scanned-angle or scanned-energy. General rules for optimizing image quality for a given data-set range are also discussed, and used to evaluate the sampling choices made in some prior experimental studies.
The current status of photoelectron-diffraction studies of surface structures is briefly reviewed... more The current status of photoelectron-diffraction studies of surface structures is briefly reviewed, and several recent developments and proposals for future areas of application are then discussed. The application of full-solid-angle diffraction data, together with simultaneous characterization by low-energy electron-diffraction and scanning-tunneling microscopy, to epitaxial growth is considered. Several new avenues that are being opened up by third-generation synchrotron-radiation sources are also considered. These include photoelectron diffraction from surface and interface atoms, the possibility of time-resolved measurements, and circular dichroism in photoelectron angular distributions. The addition of spin to the photoelectron-diffraction measurement is also considered, and can be achieved either through core-level multiplet splittings or by circular-polarized excitation of spin–orbit-split levels. This last development should make it possible to study short-range magnetic orde...
Journal of Electron Spectroscopy and Related Phenomena, 1995
ABSTRACT Images of near-surface atoms can be obtained from photoelectron diffraction data by vari... more ABSTRACT Images of near-surface atoms can be obtained from photoelectron diffraction data by various imaging algorithms, the basic method being: (a) a Fourier transform over k-space involving a path-length difference phase factor. We will also discuss two recently proposed direct methods that compensate for the non-optical atomic scattering of photoelectrons: (b) a Fourier transform of small k-space cones centered on the approximately optical scattering regions of a photoelectron diffraction data set; and (c), a truly quantum mechanical Fourier transform that accounts for the non-optical propagation and atomic scattering of the photoelectrons in the first Born approximation. Atomic images produced by these three methods are compared for photoelectron diffraction patterns calculated from a single scattering Ni trimer, and a large multiple scattering Ni bulk cluster. All three methods are found to comparably resolve backscattering atomic images, while poorly resolving forward and side scattering atomic images.
... From that point through the rest of the semester, student interaction during review questions... more ... From that point through the rest of the semester, student interaction during review questions was much more animated, with a marked increase in discussion among students and within small groups. ...Astronomy 10 is a one-semester survey course at Cuesta College. ...
In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT)... more In this paper we present a complete description of the breathing synchronized radiotherapy (BSRT) system, which has been jointly developed between the University of California Davis Cancer Center and Varian Associates. BSRT is a description of an emerging radiation oncology procedure, where simulation, CT scan, treatment planning, and radiation treatment are synchronized with voluntary breath‐hold, forced breath‐hold, or breathing gating. The BSRT system consists of a breathing monitoring system (BMOS) and a linear accelerator gating hardware and software package. Two methods, a video camera‐based method and the use of wraparound inductive plethysmography (RespiTrace), generate the BMOS signals. The BMOS signals and the synchronized fluoroscopic images are simultaneously recorded in the simulation room and are later analyzed to define the ideal treatment point (ITP) where organ motion is stationary. The BMOS signals at ITP can be used to gate a CT scanner or a linear accelerator to ...
International Journal of Radiation Oncology*Biology*Physics, 1999
Selective gene expression in response to the tumor-specific microenvironment may provide new aven... more Selective gene expression in response to the tumor-specific microenvironment may provide new avenues for cancer treatment. In this study, we have established a hypoxia inducible vector system for specific production of therapeutic genes in tumors and have assessed its in vitro and in viva efficacy.
ABSTRACT A complete angle- and energy-dependent photoelectron diffraction data set has been measu... more ABSTRACT A complete angle- and energy-dependent photoelectron diffraction data set has been measured for bulk and surface 4f core-level emission from clean W(110). This data set, the largest for a surface core-level to date, consists of uniform sampling over a large k-space range encompassing nearly 2pi emission angles with 0.1 inverse Angstrom momentum steps. Volume representations of the data visually highlight the transition from multiple- scattering to back-scattering energy regimes. These high density data sets, taken at the high-brightness undulator soft x-ray beamline 7.0 at the Advanced Light Source, provide a stringent test for electron-scattering simulations and for direct holographic inversion algorithms. Most photoelectron holography experiments to date have used an approximation to a three-dimensional Fourier integral due to coarse sampling in either angles or energy. Comparison will be made of experiment to single- and multiple-scattering theories; and a comparison of four different holographic inversion algorithms will be presented.
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