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Friday, June 25, 2012

John Thornton
Air Vehicles Division, Department of Defense, Australia

"TBA"

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Friday, June 22, 2012

Rob McKenna
University of Florida

"TBA"

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****NOTE: Day & Time****

Wednesday, May 23, 2012
Time: 9am

Jacob Ruff
The Advanced Photon Source, Argonne National Laboratory

"Shining Light on Materials in High Magnetic Fields"

Abstract:  In this talk, I will review recent efforts at the Advanced Photon Source to establish a suite of capabilities for synchrotron x-ray scattering in applied magnetic fields as high as 30 Tesla^[1-3]. The combination of custom-built magnets and synchrotron light sources offers a unique microscopic perspective on the magnetoelastic properties of materials, which we are now learning to exploit. As an example of the science enabled by these efforts, I will present diffraction measurements of an iron arsenide superconductor in pulsed magnetic fields^[4]. This orthorhombic crystal is shown to exhibit dynamic de-twinning driven by a pronounced anisotropy in the magnetic susceptibility. Tracking the non-trivial temperature dependence of this effect allows us to put new constraints on theories of "nematic" electronic phases in the iron arsenides. Potential future directions for novel studies of magnetic materials at synchrotrons will also be discussed, time permitting.

References:
[1] Z. Islam et al.; “A Portable High-field Pulsed-magnet System for Single-crystal X-ray Scattering Studies”, Rev. Sci. Instrum. 80, 113902 (2009)

[2] Z. Islam et al.; “A Single-solenoid Pulsed-magnet System for Single-Crystal Scattering Studies”, Rev. Sci. Instrum. 83, 035101 (2012)

[3] J.P.C. Ruff et al.; “Magnetoelastics of a Spin Liquid: X-Ray Diffraction Studies of Tb2Ti2O7 in Pulsed Magnetic Fields”, Phys. Rev. Lett. 105, 077203 (2010)

[4] J.P.C. Ruff et al.; “Susceptibility Anisotropy in an Iron Arsenide Superconductor Revealed by X-ray Diffraction in Pulsed Magnetic Fields”, arXiv:1204.5693v1 (2012)

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****NOTE: Day & Time****

Wednesday, May 9, 2012
Time: 9am

Jun-Sang Park
Cornell University

"Understanding the State of Polycrystalline Structural Alloys using High Energy Synchrotron X-rays"

Abstract:  As the demand for efficient, high-performance machines increases, quantifying the state of materials and understanding their micro-mechanical behavior are ever more important for designing and building these machines. High energy synchrotron radiation is an attractive tool for investigating the state and the micromechanical behavior of polycrystalline structural alloys. In this talk, two techniques will be presented.

In the first part of the talk, a method for quantifying the residual stress field in a polycrystalline material is described. An experimental setup that combines monochromatic high energy x-ray diffraction and a set of conical slits is described. The set of conical slits allows the non-destructive measurement of lattice strains for diffraction volumes located inside the material and is used to measure the strain pole figures (SPFs) for diffraction volumes located inside a polycrystalline component. Full three-dimensional residual stress field is determined by a bi-scale optimization scheme. In this scheme, the residual stress field satisfies the SPF measurements at the crystal length scale. At the macroscopic length scale, the residual stress field also satisfies equilibrium and imposed boundary conditions. To demonstrate the new method, a polycrystalline shrink-fit sample with a three-dimensional stress gradient was manufactured from a low solvus high refractory (LSHR) Ni-based superalloy. The residual stress field determined using the new method compares favorably with an analytic approximation of the stresses within the shrink-fit sample.

In the second part of the talk, a framework for understanding the micromechanical behavior of individual crystals embedded in a polycrystalline aggregate is described. This framework combines the synchrotron x-ray experiments and the polycrystal finite element simulation to understand the micromechanical behavior. A method for simulating diffraction spots from individual virtual crystals using the information obtained from a polycrystal finite element simulation is described. To demonstrate the method, a set of high energy diffraction data were collected while applying a uniaxial tension on a high strength copper specimen. The diffraction data were analyzed to determine the orientations and the stresses of the crystals in the diffraction volume. The crystal orientations were used to instantiate a virtual polycrystal and a slip-based polycrystal finite element simulations were performed. Using the information obtained from the finite element simulations, a set of virtual diffraction spots is generated. These virtual diffraction spots are compared to the experimental diffraction spots.

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****NOTE: Day & Time****

Wednesday, May 2, 2012
Time: 9am

Dr. Pamela Whitfield
National Research Council Canada

"Advanced Powder Diffraction with Lab Instrumentation
- or doing things the hard way!"

Abstract:  I intend giving an overview of some of the different work that I’ve carried out at ICPET over the past number of years. Although the subject materials differ significantly (lithium battery cathode material, organic and minerals), powder diffraction is the thread that runs through all of the studies. Synchrotron and neutron diffraction also feature but the majority of the work was carried out using laboratory-based instrumentation. The facility at ICPET is very well equipped and the instrumentation setups are generally highly specialized and unusual for lab systems. In-situ and non-ambient measurements are of particular interest and where commercial equipment didn’t exist we designed and often built or assembled it in-house. Overcoming the challenges of lab diffractometers in terms of cramped space, limited number of wavelengths and not upsetting the radiation safety officer by drilling holes everywhere are all ongoing problems. A number of the topics involve such custom built sample environments where the designs overcome different issues and sometimes turn problems into positive advantages.

I intend covering the first 3 topics but can swap topics with the last 2 depending on interest...

• Complex refinement of cation-ordering in lithium battery materials using resonant and neutron powder diffraction
• Preferential orientation and structure determination from powder diffraction (SDPD)
• Custom in-situ gas pressure cells for lab diffractometers and synchrotrons
• Cleaner data from in-situ battery studies – new variable temperature stage, pouch cell design and application of grazing incidence diffraction
• Kryptonite - structure solution from powder diffraction data

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Friday, April 27, 2012

Fareh Pei-Jen Lin
Old Dominion University

Abstract:  We consider the effect of non-magnetic and magnetic impurities on the superheating field Hs in type-II superconductors. We solve the Eilenberger equations, which take into account the non-linear pairbreaking of Meissner screening currents, and calculate the superheating field for arbitrary temperatures and impurity concentrations in a single-band S-wave superconductor with a large Ginzburg-Landau parameter. At low temperatures non-magnetic impurities suppress a weak maximum in H_s (T ) which has been predicted for the clean limit, resulting instead in a maximum of H_s as a function of impurity concentration near clean limit. It is shown that non-magnetic impurities weakly affect H_s even in the dirty limit of large scattering rate, α ≫ 1. However, magnetic impurities suppress both H_s and the critical temperature T_c. The density of quasiparticle states N (Є) is strongly affected by an interplay of impurity scattering and current pairbreaking. We show that a clean superconductor at H = H_s is in a gapless state, but a quasiparticle gap Є_g in N (Є) at H = H_s appears as the concentration of non-magnetic impurities increases. As the non-magnetic scattering rate increases above α_c = 0.36, the quasiparticle gap Є_g (α) at H = H_s increases, approaching Є_g ≈ 0.32∆₀ in the dirty limit, where ∆₀ is the superconducting gap parameter at zero field. The effects of impurities on Hs can be essential for understanding non-linear surface resistance and superconductivity breakdown by strong RF fields.

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Friday, April 13, 2012

Dr. Konstantin Lekomtsev
University of London

"Coherent Diffraction Radiation as a Tool for Non-invasive Bunch Length Diagnostics"

Abstract:  In this seminar I will discuss Coherent Diffraction Radiation (CDR) phenomenon as a tool for longitudinal beam diagnostics. Precise knowledge of a longitudinal bunch profile is particularly important in the context of the luminosity challenge in the future linear colliders and therefore the development of a non-invasive and robust longitudinal beam diagnostic technique is very important.

CDR is emitted when a bunch of charged particles moves in the vicinity of an optical obstacle (for example a screen, or a slit between screens) and the wavelength of the radiation is larger or comparable to the bunch length. CDR has been experimentally investigated over the period of the last 20 years and has been proven to be very promising candidate for longitudinal diagnostics, due to its non-invasive nature and high radiation intensity.

During the course of the seminar I will discuss a novel two-target scheme for the CDR generation. The experimental demonstration of this scheme is a setup installed at the CLIC Test Facility (CTF3) at CERN. A new theoretical model which was developed specifically for the dual-target experimental setup will also be presented and compared with experimental data. The main concepts of the longitudinal diagnostics based on the analysis of the CDR spectrum will be introduced. The limitations of the Kramers-Kronig technique as a tool for bunch profiling, and Coherent Synchrotron Radiation background contribution in the CDR spatial distribution will be discussed.

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Friday, April 6, 2012

He Zhang
Michigan State University

"Fast Multipole Algorithm Using Differential Algebra for Space Charge Field Calculation and Low Emittance Lattice Design for Hefei Light Source Storage Ring"

Abstract:  A variant of the fast multipole method (FMM) using differential algebra will be presented. This algorithm allows the computation of the self-field for arbitrary and large distributions of charged particles in an efficient and accurate way. Given an ensemble of N particles, the computational expense scales as O(N). Some numerical examples of applying the algorithm in beam dynamic simulation will be presented.

A four-folded low emittance lattice for Hefei Light Source electron storage ring, which decreases the emittance from 166 nm*rad to 16 nm*rad, was proposed. Related beam dynamic topics, such as on momentum and off momentum dynamics, close orbit distortion and compensation, effects of insertion devices, are discussed.

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Friday, March 16, 2012

Alex Deyheim
ADC

"Advanced Design Consulting, Current Projects, Future Possibilities"

Abstract:  ADC offers a large assortment of synchrotron equipment including; High Precision Slits, Optical Tables, Micro Ion Chambers, Split Two Axis Ion Chambers, Mirror Systems, Monochromators, Spectrometers, Insertion Devices (EPU, Wiggler, Planar, In-Vacuum, Apple), ID Measurement System and many other Beamline Components.  Alex will discuss the following:

1. A summary of Synchrotron Related Systems delivered and/or under construction for facilities around the world (APS, NSLS   and NSLS II, ALS, DLS, NSRRC, BESSY, DESY, CHESS, ESRF, BSRF, CAMD, NSRL, PAL, SSRF, IHEP, ANKA, KEK, ASP, SPring-8, ELETTRA, MAXLab, …)

2. A summary of ADC’s History, sales volume, staffing….

3. A summary of ADC’s facilities, equipment, capabilities (UHV capabilities, testing…)

4. Describing ADC’s operation

5. A summary of ADC’s High Precision Slits

6. A summary of Synchrotron Beamline Components

7. A summary of Insertion Devices delivered and under construction

8. A summary of ADC’s Standard Motion Systems (Linear Stages, Goniometers, Vertical Jacks, Rotation stages)

9. A summary of Custom High Precision Motion Systems ADC has delivered

10. A summary of ADC’s Standard Optical Tables

11. ADC’s Control & Electronic Capabilities

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****NOTE: Day****

Thursday, March 1, 2012

Dimitre Dimitrov
Tech-X

"Modeling and Simulations of Charge Carrier Effects in Diamond and GaAs for Cathode Applications"

Abstract:  High-fidelity modeling and simulations of electron emission physics are needed to better understand and address cathode-related issues. I will review work we have done to develop and implement algorithms in the VORPAL three-dimensional particle-in-cell code for modeling charge gain, transport, and emission from diamon-amplified cathodes. Emission of electrons in diamond experiments based on the promising diamond-amplifier concept was recently demonstrated. However, these emission experiments indicate that surface effects should be understood in detail to build cathodes with optimal properties. Transmission mode experiments have shown the potential to realize over two orders of magnitude charge amplification. We have made progress in understanding secondary electron generation and charge transport in diamond transmission-mode experiments with models we implemented in VORPAL. We have started to investigate algorithms for surface effects (band bending and electron affinity), charge trapping, and electron emission from diamond. I will present and discuss results from 3D VORPAL diamond-vacuum simulations with the integrated capabilities on generating electrons and holes, charge transport, and then emission of electrons from diamond into vacuum. Recently, we have also started to add capabilities for simulation of charge transport in a three-band GaAs. Results from GaAs simulations with these capabilities will also be presented and their relevance to cathode-related experiments will be discussed.

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Friday, February 17, 2012

Dr. Julian Becker
DESY

Presentation:  (Pdf)

"Towards the Perfect Imager: Detector developments for next generation X-ray sources"

Abstract:  I will be starting with a short overview of our group’s activities to develop detectors for PETRA III, the world’s most brilliant synchrotron source, located on the DESY premises.

New challenges arise for detector builders when designing detectors for Free Electron Laser (FEL) sources. I will introduce the European XFEL, currently under construction at DESY, and the special requirements it puts on detector projects like the Adaptive Gain Integration Pixel Detector (AGIPD).

I will close with an example of the challenges and possibilities for X-ray photon correlation spectroscopy (XPCS) at the European XFEL using the AGIPD.

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Friday, February 3, 2012

David Schuller, Staff Scientist
MacCHESS, Cornell University

"Phasing of Quasi-racemic Protein Diffraction"

Presentation: Pdf

Abstract:  Dr. Schuller will be discussing 2 papers which are listed below:
1)  "X-ray Structure of Snow Flea Antifreeze Protein Determined by Racemic Crystallization of Synthetic Protein Enantiomers", Brad L. Pentelute, Zachary P. Gates, Valentina Tereshko, Jennifer Dashnau, Jane M. Vanderkooi, Anthony A. Kossiakoff, and Stephen B. H. Kent; J Am Chem Soc, 130, 9695-9701 (2008) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2719301/?tool=pubmed

2)  "Single-wavelength Phasing Strategy for Quasi-racemic Protein Crystal Diffraction Data", MR Sawaya, BL Pentelute, SB Kent, and TO Yeates; Acta Crystallography. Sec D, 68: 62-8 (2012) http://scripts.iucr.org/cgi-bin/paper?S0907444911049985

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Friday, January 27, 2012

Darby Harris, Postdoc
Department of Plant Pathology and CHESS, Cornell University

"Cellulose Microfibril Crytallinity is Reduced by Mutating C-terminal Transmembrane Region Residues CESA1-A903V and CESA3-T942I"

Abstract:  The mechanisms underlying the biosynthesis of cellulose in plants are complex and still poorly understood. A central question concerns the mechanism of microfibril structure and how this is linked to the catalytic polymerization action of cellulose synthase (CESA). Furthermore, it remains unclear whether modification of cellulose microfibril structure can be achieved genetically, which could be transformative in a bio-based economy. To explore these processes in planta, we developed a chemical genetic toolbox of pharmacological inhibitors and corresponding resistance-conferring point mutations in the C-terminal transmembrane domain region of CESA1-A903V and CESA3-T942I in Arabidopsis thaliana. Using 13C solid-state nuclear magnetic resonance spectroscopy and synchrotron X-ray diffraction, we show that the cellulose microfibrils displayed reduced width and an additional cellulose C4 peak indicative of a degree of crystallinity that is intermediate between the surface and interior glucans of wild-type, suggesting a difference in glucan chain association during microfibril formation. Consistent with measurements of lower microfibril crystallinity, cellulose extracts from mutated CESA1A903V and CESA3T942I displayed greater saccharification efficiency than wild-type. Using live-cell imaging to track fluorescently labeled CESA, we found that these mutants show increased CESA velocities in the plasma membrane, an indication of increased polymerization rate. Collectively, these data suggest that CESA1A903V and CESA3T942I have modified microfibril structure in terms of crystallinity and suggest that in plants, as in bacteria, crystallization biophysically limits polymerization.

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Friday, January 20, 2012

Etienne Forest
KEK

Abstract:  In 1987, I tried to explain the difference between a horizontally integrated code and a vertically integrated tracking code. Today, I like to call them democratic and totalitarian. The concept of the totalitarian code was perhaps invented by R. Talman who referred to TEAPOT as “exact”.  Embracing Talman’s concept, I added the claim that Courant-Snyder theory is its universal doctrine. Courant-Snyder is the party propaganda in its purest form.

I will explain these concepts using spin as an example, the delusional papers that we published, and “PTC“ (the North Korea of codes).

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