HREM studies of intergrowths in Sr2[Srn-1TinO3n+1] Ruddlesden-Popper phases synthesized by mechanochemical activation

A mechanochemical activation route has been applied in order to obtain the <i>n</i>=1–4 and ∞ members of the Sr<sub>2</sub>[Sr<sub>n</sub><sub>−1</sub>Ti<sub>n</sub>O<sub>3n+1</sub>] Ruddlesden– Popper series from different (<i>n</i>+1)SrO:nTiO<sub>2</sub> mixtures. The mechanosynthesis of SrTiO<sub>3</sub> and Sr<sub>2</sub>TiO<sub>4</sub> was observed during the milling process from the initial stoichiometric mixture, but in the cases of the <i>n</i>=2–4 members, a subsequent thermal treatment was needed. The synthesis protocol of Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> has been greatly improved and this compound can be isolated as a single, crystalline phase after annealing at 800°C. In the case of Sr<sub>4</sub>Ti<sub>3</sub>O<sub>10</sub> and Sr<sub>5</sub>Ti<sub>4</sub>O<sub>13</sub>, the formation temperature was also decreased, but members with <i>n</i>=3 and 4 could not be isolated. Detailed investigations using electron microscopy methods (TEM, HREM and SAED) were carried out in the samples corresponding to <i>n</i>=2–4. Although a single ordered Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> structure is dominant in the sample corresponding to <i>n</i>=2, a few intergrowths of other Ruddlesden–Popper phases were observed. In the cases of <i>n</i>=3 and 4, the intergrowths of Ruddlesden–Popper phases are more frequent than in the <i>n</i>=2 composition and are randomly distributed in the sample. The more frequent occurrence of such stacking faults, with increasing <i>n</i> value, leads to a somewhat disordered layer stacking sequence

ANOMALOUS GAUGE BOSON INTERACTIONS

We discuss the direct measurement of the trilinear vector boson couplings in present and future collider experiments. The major goals of such experiments will be the confirmation of the Standard Model (SM) predictions and the search for signals of new physics. We review our current theoretical understanding of anomalous trilinear gauge boson self-interactions. If the energy scale of the new physics is $\sim 1$ TeV, these low energy anomalous couplings are expected to be no larger than ${\cal O}(10^{-2})$. Constraints from high precision measurements at LEP and low energy charged and neutral current processes are critically reviewed.Comment: 53 pages with 17 embedded figures, LaTeX, uses axodraw.sty, figures available on request. The complete paper, is available at ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z or http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z Summary of the DPF Working Subgroup on Anomalous Gauge Boson Interactions of the DPF Long Range Planning Stud

Powder diffraction in the range of milliseconds

Powder diffraction studies with synchrotron radiation were performed on a time scale down to 2.5 ms at the HASYLAB beamline B2 with a commercial 1024 pixel linear photodiode-array detector system (OMA III, EG&G-PARC). The flux rate of 2 x 108 photons s-1 at a wavelength of 1.26 Å achieved by using a toroidal mirror and a standard double-crystal Si(111) monochromator was measured with an ionization chamber at the focus. With a synthetic multilayer to select the desired wavelength instead of the standard monochromator, a flux rate of 1.5 x 1010 photons s-1 was measured at a wavelength of 1.31 Å. The shortest possible recording times for a complete powder pattern of calcium fluoride were 200 ms with the crystal monochromator and 2.5 ms with the multilayer. The angular resolution for both cases is discussed. The high-speed data collection was successfully applied with the double-crystal and multilayer monochromators to the recording of more-complex patterns and to monitor a phase transformation in order to demonstrate the feasibility of kinetic studies on the millisecond time scale

WW and WZ production at the tevatron

Direct limits are set on WWZ and WW{gamma} three-boson couplings in a search for WW and WZ production in p{bar p} collisions at {radical}s = 1.8 TeV using the D(0) and CDF detectors at the Fermilab Tevatron

Experimental magnetic form factors in Co3V2O8: A combined study of ab initio calculations, magnetic Compton scattering and polarized neutron diffraction

We present a combination of ab initio calculations, magnetic Compton scattering and polarized neutron experiments, which elucidate the density distribution of unpaired electrons in the kagome staircase system Co3V2O8. Ab initio wave functions were used to calculate the spin densities in real and momentum space, which show good agreement with the respective experiments. It has been found that the spin polarized orbitals are equally distributed between the t2g and the eg levels for the spine (s) Co ions, while the eg orbitals of the cross-tie (c) Co ions only represent 30% of the atomic spin density. Furthermore, the results reveal that the magnetic moments of the cross-tie Co ions, which are significantly smaller than those of the spine Co ions in the zero-field ferromagnetic structure, do not saturate by applying an external magnetic field of 2 T along the easy axis a, but that the increasing bulk magnetization originates from induced magnetic moments on the O and V sites. The refined individual magnetic moments are mu(Co_c)=1.54(4) mu_B, mu(Co_s)=2.87(3) mu_B, mu(V)=0.41(4) mu_B, mu(O1)=0.05(5) mu_B, mu(O2)=0.35(5) mu_B, and; mu(O3)=0.36(5) mu_B combining to the same macroscopic magnetization value, which was previously only attributed to the Co ions

Experimental measurement of stress at a four-domain junction in lead zirconate titanate

A junction between two lamellar bands of ferroelectric domains in a lead zirconate titanate (PZT) ceramic is analysed using Kikuchi diffraction patterns in the transmission electron microscope. Indexing of the diffraction patterns allowed the determination of the 3D relative orientation of the 4 different domains at the junction and thus the characterisation of the domain boundaries. The local c/a ratio could also be determined from the misorientations at the domain boundaries. Analysis of the data showed that large stresses were concentrated at the junction, and that this is inevitable at such band junctions. Such stress concentrations could act as nuclei for cracking of the ceramic under additional loading in service, perhaps particularly as a consequence of extended electromechanical cycling. Moreover, the stresses would increase with increasing c/a making the issues all the more serious for Ti-rich compositions having larger c/a ratios

Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8

The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been measured as function of temperature and magnetic field up to 14T. It is found that the application of an external magnetic field suppresses the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic field dependence reveals a negative magnetocapacitance which is proportional to the magnetic susceptibility, suggesting a common magnetostrictive origin for the magnetic field dependence of the two quantities. This result is very different from that obtained from the isostructural compound Ni3V2O8 that presents a peak in the dielectric constant at the incommensurate magnetic phase transition coupled to a sign change of the magnetocapacitance

HEPCloud, a New Paradigm for HEP Facilities: CMS Amazon Web Services Investigation

Historically, high energy physics computing has been performed on large purpose-built computing systems. These began as single-site compute facilities, but have evolved into the distributed computing grids used today. Recently, there has been an exponential increase in the capacity and capability of commercial clouds. Cloud resources are highly virtualized and intended to be able to be flexibly deployed for a variety of computing tasks. There is a growing nterest among the cloud providers to demonstrate the capability to perform large-scale scientific computing. In this paper, we discuss results from the CMS experiment using the Fermilab HEPCloud facility, which utilized both local Fermilab resources and virtual machines in the Amazon Web Services Elastic Compute Cloud. We discuss the planning, technical challenges, and lessons learned involved in performing physics workflows on a large-scale set of virtualized resources. In addition, we will discuss the economics and operational efficiencies when executing workflows both in the cloud and on dedicated resources.Comment: 15 pages, 9 figure

Scintillation Counters for the D0 Muon Upgrade

We present the results of an upgrade to the D0 muon system. Scintillating counters have been added to the existing central D0 muon system to provide rejection for cosmic ray muons and out-of-time background, and to provide additional fast timing information for muons in an upgraded Tevatron. Performance and results from the 1994-1996 Tevatron run are presented.Comment: 30 pages, 25 postscript figure

ASCR/HEP Exascale Requirements Review Report

This draft report summarizes and details the findings, results, and recommendations derived from the ASCR/HEP Exascale Requirements Review meeting held in June, 2015. The main conclusions are as follows. 1) Larger, more capable computing and data facilities are needed to support HEP science goals in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of the demand at the 2025 timescale is at least two orders of magnitude -- and in some cases greater -- than that available currently. 2) The growth rate of data produced by simulations is overwhelming the current ability, of both facilities and researchers, to store and analyze it. Additional resources and new techniques for data analysis are urgently needed. 3) Data rates and volumes from HEP experimental facilities are also straining the ability to store and analyze large and complex data volumes. Appropriately configured leadership-class facilities can play a transformational role in enabling scientific discovery from these datasets. 4) A close integration of HPC simulation and data analysis will aid greatly in interpreting results from HEP experiments. Such an integration will minimize data movement and facilitate interdependent workflows. 5) Long-range planning between HEP and ASCR will be required to meet HEP's research needs. To best use ASCR HPC resources the experimental HEP program needs a) an established long-term plan for access to ASCR computational and data resources, b) an ability to map workflows onto HPC resources, c) the ability for ASCR facilities to accommodate workflows run by collaborations that can have thousands of individual members, d) to transition codes to the next-generation HPC platforms that will be available at ASCR facilities, e) to build up and train a workforce capable of developing and using simulations and analysis to support HEP scientific research on next-generation systems.Comment: 77 pages, 13 Figures; draft report, subject to further revisio