Improvements in Ionized Cluster-Beam Deposition

NASA Technical Reports Server (NTRS)

Fitzgerald, D. J.; Compton, L. E.; Pawlik, E. V.

1986-01-01

Lower temperatures result in higher purity and fewer equipment problems. In cluster-beam deposition, clusters of atoms formed by adiabatic expansion nozzle and with proper nozzle design, expanding vapor cools sufficiently to become supersaturated and form clusters of material deposited. Clusters are ionized and accelerated in electric field and then impacted on substrate where films form. Improved cluster-beam technique useful for deposition of refractory metals.

Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

NASA Astrophysics Data System (ADS)

Podestà, Alessandro; Borghi, Francesca; Indrieri, Marco; Bovio, Simone; Piazzoni, Claudio; Milani, Paolo

2015-12-01

Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO2) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevant interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.

Nanomanufacturing of titania interfaces with controlled structural and functional properties by supersonic cluster beam deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Podestà, Alessandro, E-mail: alessandro.podesta@mi.infn.it, E-mail: pmilani@mi.infn.it; Borghi, Francesca; Indrieri, Marco

Great emphasis is placed on the development of integrated approaches for the synthesis and the characterization of ad hoc nanostructured platforms, to be used as templates with controlled morphology and chemical properties for the investigation of specific phenomena of great relevance in interdisciplinary fields such as biotechnology, medicine, and advanced materials. Here, we discuss the crucial role and the advantages of thin film deposition strategies based on cluster-assembling from supersonic cluster beams. We select cluster-assembled nanostructured titania (ns-TiO{sub 2}) as a case study to demonstrate that accurate control over morphological parameters can be routinely achieved, and consequently, over several relevantmore » interfacial properties and phenomena, like surface charging in a liquid electrolyte, and proteins and nanoparticles adsorption. In particular, we show that the very good control of nanoscale morphology is obtained by taking advantage of simple scaling laws governing the ballistic deposition regime of low-energy, mass-dispersed clusters with reduced surface mobility.« less

Study on the coloration response of a radiochromic film to MeV cluster ion beams

NASA Astrophysics Data System (ADS)

Yuri, Yosuke; Narumi, Kazumasa; Chiba, Atsuya; Hirano, Yoshimi; Saitoh, Yuichi

2017-11-01

A radiochromic film, Gafchromic HD-V2, is applied to a possible method of measuring a two-dimensional (2D) spatial profile of MeV cluster ion beams. The coloration responses of the HD-V2 film to MeV carbon and gold cluster ion beams are experimentally investigated since some cluster effect may appear. The degree of the film coloration is quantified as a change in optical density (OD) by reading the films with an image scanner for high-resolution measurement of the 2D beam profile. The OD response of HD-V2 is characterized as a function of the ion and atom fluence for comparison. The dependences of the OD response on the cluster size, kinetic energy, and ion species are discussed. It is found that the sensitivity of the OD change is reduced when the cluster size is large. The beam profile of MeV cluster ion beams delivered from the tandem accelerator in TIARA is characterized from the measurement result using HD-V2 films. The present results show that the use of the Gafchromic HD-V2 film is suitable for the detail beam profile measurement of MeV cluster ions, especially C60 ions, whose available intensity is rather low in comparison with that of monatomic ion beams.

Dynamic secondary ion mass spectroscopy of Au nanoparticles on Si wafer using Bi3+ as primary ion coupled with surface etching by Ar cluster ion beam: The effect of etching conditions on surface structure

NASA Astrophysics Data System (ADS)

Park, Eun Ji; Choi, Chang Min; Kim, Il Hee; Kim, Jung-Hwan; Lee, Gaehang; Jin, Jong Sung; Ganteför, Gerd; Kim, Young Dok; Choi, Myoung Choul

2018-01-01

Wet-chemically synthesized Au nanoparticles were deposited on Si wafer surfaces, and the secondary ions mass spectra (SIMS) from these samples were collected using Bi3+ with an energy of 30 keV as the primary ions. In the SIMS, Au cluster cations with a well-known, even-odd alteration pattern in the signal intensity were observed. We also performed depth profile SIMS analyses, i.e., etching the surface using an Ar gas cluster ion beam (GCIB), and a subsequent Bi3+ SIMS analysis was repetitively performed. Here, two different etching conditions (Ar1600 clusters of 10 keV energy or Ar1000 of 2.5 keV denoted as "harsh" or "soft" etching conditions, respectively) were used. Etching under harsh conditions induced emission of the Au-Si binary cluster cations in the SIMS spectra of the Bi3+ primary ions. The formation of binary cluster cations can be induced by either fragmentation of Au nanoparticles or alloying of Au and Si, increasing Au-Si coordination on the sample surface during harsh GCIB etching. Alternatively, use of the soft GCIB etching conditions resulted in exclusive emission of pure Au cluster cations with nearly no Au-Si cluster cation formation. Depth profile analyses of the Bi3+ SIMS combined with soft GCIB etching can be useful for studying the chemical environments of atoms at the surface without altering the original interface structure during etching.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altunbas, Cem, E-mail: caltunbas@gmail.com; Lai, Chao-Jen; Zhong, Yuncheng

Purpose: In using flat panel detectors (FPD) for cone beam computed tomography (CBCT), pixel gain variations may lead to structured nonuniformities in projections and ring artifacts in CBCT images. Such gain variations can be caused by change in detector entrance exposure levels or beam hardening, and they are not accounted by conventional flat field correction methods. In this work, the authors presented a method to identify isolated pixel clusters that exhibit gain variations and proposed a pixel gain correction (PGC) method to suppress both beam hardening and exposure level dependent gain variations. Methods: To modulate both beam spectrum and entrancemore » exposure, flood field FPD projections were acquired using beam filters with varying thicknesses. “Ideal” pixel values were estimated by performing polynomial fits in both raw and flat field corrected projections. Residuals were calculated by taking the difference between measured and ideal pixel values to identify clustered image and FPD artifacts in flat field corrected and raw images, respectively. To correct clustered image artifacts, the ratio of ideal to measured pixel values in filtered images were utilized as pixel-specific gain correction factors, referred as PGC method, and they were tabulated as a function of pixel value in a look-up table. Results: 0.035% of detector pixels lead to clustered image artifacts in flat field corrected projections, where 80% of these pixels were traced back and linked to artifacts in the FPD. The performance of PGC method was tested in variety of imaging conditions and phantoms. The PGC method reduced clustered image artifacts and fixed pattern noise in projections, and ring artifacts in CBCT images. Conclusions: Clustered projection image artifacts that lead to ring artifacts in CBCT can be better identified with our artifact detection approach. When compared to the conventional flat field correction method, the proposed PGC method enables characterization of nonlinear pixel gain variations as a function of change in x-ray spectrum and intensity. Hence, it can better suppress image artifacts due to beam hardening as well as artifacts that arise from detector entrance exposure variation.« less

Measurement of track structure parameters of low and medium energy helium and carbon ions in nanometric volumes

NASA Astrophysics Data System (ADS)

Hilgers, G.; Bug, M. U.; Rabus, H.

2017-10-01

Ionization cluster size distributions produced in the sensitive volume of an ion-counting wall-less nanodosimeter by monoenergetic carbon ions with energies between 45 MeV and 150 MeV were measured at the TANDEM-ALPI ion accelerator facility complex of the LNL-INFN in Legnaro. Those produced by monoenergetic helium ions with energies between 2 MeV and 20 MeV were measured at the accelerator facilities of PTB and with a 241Am alpha particle source. C3H8 was used as the target gas. The ionization cluster size distributions were measured in narrow beam geometry with the primary beam passing the target volume at specified distances from its centre, and in broad beam geometry with a fan-like primary beam. By applying a suitable drift time window, the effective size of the target volume was adjusted to match the size of a DNA segment. The measured data were compared with the results of simulations obtained with the PTB Monte Carlo code PTra. Before the comparison, the simulated cluster size distributions were corrected with respect to the background of additional ionizations produced in the transport system of the ionized target gas molecules. Measured and simulated characteristics of the particle track structure are in good agreement for both types of primary particles and for both types of the irradiation geometry. As the range in tissue of the ions investigated is within the typical extension of a spread-out Bragg peak, these data are useful for benchmarking not only ‘general purpose’ track structure simulation codes, but also treatment planning codes used in hadron therapy. Additionally, these data sets may serve as a data base for codes modelling the induction of radiation damages at the DNA-level as they almost completely characterize the ionization component of the nanometric track structure.

CO2 Cluster Ion Beam, an Alternative Projectile for Secondary Ion Mass Spectrometry

NASA Astrophysics Data System (ADS)

Tian, Hua; Maciążek, Dawid; Postawa, Zbigniew; Garrison, Barbara J.; Winograd, Nicholas

2016-09-01

The emergence of argon-based gas cluster ion beams for SIMS experiments opens new possibilities for molecular depth profiling and 3D chemical imaging. These beams generally leave less surface chemical damage and yield mass spectra with reduced fragmentation compared with smaller cluster projectiles. For nanoscale bioimaging applications, however, limited sensitivity due to low ionization probability and technical challenges of beam focusing remain problematic. The use of gas cluster ion beams based upon systems other than argon offer an opportunity to resolve these difficulties. Here we report on the prospects of employing CO2 as a simple alternative to argon. Ionization efficiency, chemical damage, sputter rate, and beam focus are investigated on model compounds using a series of CO2 and Ar cluster projectiles (cluster size 1000-5000) with the same mass. The results show that the two projectiles are very similar in each of these aspects. Computer simulations comparing the impact of Ar2000 and (CO2)2000 on an organic target also confirm that the CO2 molecules in the cluster projectile remain intact, acting as a single particle of m/z 44. The imaging resolution employing CO2 cluster projectiles is improved by more than a factor of two. The advantage of CO2 versus Ar is also related to the increased stability which, in addition, facilitates the operation of the gas cluster ion beams (GCIB) system at lower backing pressure.

Nuclear structure studies with gamma-ray beams

DOE PAGES

Tonchev, Anton; Bhatia, Chitra; Kelley, John; ...

2015-05-28

In stable and weakly bound neutron-rich nuclei, a resonance-like concentration of dipole states has been observed for excitation energies below the neutron-separation energy. This clustering of strong dipole states has been named the Pygmy Dipole Resonance (PDR) in contrast to the Giant Dipole Resonance (GDR) that dominates the E1 response. Understanding the PDR is presently of great interest in nuclear structure and nuclear astrophysics. High-sensitivity studies of E1 and M1 transitions in closed-shell nuclei using monoenergetic and 100% linearly-polarized photon beams are presented.

Nuclear Structure Studies with Gamma-Ray Beams

NASA Astrophysics Data System (ADS)

Tonchev, Anton; Bhatia, Chitra; Kelley, John; Raut, Rajarshi; Rusev, Gencho; Tornow, Werner; Tsoneva, Nadia

2015-05-01

In stable and weakly bound neutron-rich nuclei, a resonance-like concentration of dipole states has been observed for excitation energies below the neutron-separation energy. This clustering of strong dipole states has been named the Pygmy Dipole Resonance (PDR) in contrast to the Giant Dipole Resonance (GDR) that dominates the E1 response. Understanding the PDR is presently of great interest in nuclear structure and nuclear astrophysics. High-sensitivity studies of E1 and M1 transitions in closed-shell nuclei using monoenergetic and 100% linearly-polarized photon beams are presented.

Atomic-scale structure and electronic properties of GaN/GaAs superlattices

NASA Astrophysics Data System (ADS)

Goldman, R. S.; Feenstra, R. M.; Briner, B. G.; O'Steen, M. L.; Hauenstein, R. J.

1996-12-01

We have investigated the atomic-scale structure and electronic properties of GaN/GaAs superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy (STM) and spectroscopy, we show that the nitrided layers are laterally inhomogeneous, consisting of groups of atomic-scale defects and larger clusters. Analysis of x-ray diffraction data in terms of fractional area of clusters (determined by STM), reveals a cluster lattice constant similar to bulk GaN. In addition, tunneling spectroscopy on the defects indicates a conduction band state associated with an acceptor level of NAs in GaAs. Therefore, we identify the clusters and defects as nearly pure GaN and NAs, respectively. Together, the results reveal phase segregation in these arsenide/nitride structures, in agreement with the large miscibility gap predicted for GaAsN.

IR + VUV double resonance spectroscopy and extended density functional theory studies of ketone solvation by alcohol: 2-butanone·(methanol)n, n = 1-4 clusters.

PubMed

Shin, Joong-Won; Bernstein, Elliot R

2017-09-28

Infrared plus vacuum ultraviolet (IR + VUV) photoionization vibrational spectroscopy of 2-butanone/methanol clusters [MEK·(MeOH) n , n = 1-4] is performed to explore structures associated with hydrogen bonding of MeOH molecules to the carbonyl functional group of the ketone. IR spectra and X3LYP/6-31++G(d,p) calculations show that multiple isomers of MEK·(MeOH) n are generated in the molecular beam as a result of several hydrogen bonding sites available to the clusters throughout the size range investigated. Isomer interconversion involving solvating MeOH rearrangement should probably occur for n = 1 and 2. The mode energy for a hydrogen bonded OH stretching transition gradually redshifts as the cluster size increases. Calculations suggest that the n = 3 cluster isomers adopt structures in which the MEK molecule is inserted into the cyclic MeOH hydrogen bond network. In larger structures, the cyclic network may be preserved.

Supersonic Bare Metal Cluster Beams. Technical Progress Report, March 16, 1984 - April 1, 1985

DOE R&D Accomplishments Database

Smalley, R. E.

1985-01-01

There have been four major areas of concentration for the study of bare metal cluster beams: neutral cluster, chemical reactivity, cold cluster ion source development (both positive and negative), bare cluster ion ICR (ion cyclotron resonance) development, and photofragmentation studies of bare metal cluster ions.

Transfer-free synthesis of graphene-like atomically thin carbon films on SiC by ion beam mixing technique

NASA Astrophysics Data System (ADS)

Zhang, Rui; Chen, Fenghua; Wang, Jinbin; Fu, Dejun

2018-03-01

Here we demonstrate the synthesis of graphene directly on SiC substrates at 900 °C using ion beam mixing technique with energetic carbon cluster ions on Ni/SiC structures. The thickness of 7-8 nm Ni films was evaporated on the SiC substrates, followed by C cluster ion bombarding. Carbon cluster ions C4 were bombarded at 16 keV with the dosage of 4 × 1016 atoms/cm2. After thermal annealing process Ni silicides were formed, whereas C atoms either from the decomposition of the SiC substrates or the implanted contributes to the graphene synthesis by segregating and precipitating process. The limited solubility of carbon atoms in silicides, involving SiC, Ni2Si, Ni5Si2, Ni3Si, resulted in diffusion and precipitation of carbon atoms to form graphene on top of Ni and the interface of Ni/SiC. The ion beam mixing technique provides an attractive production method of a transfer-free graphene growth on SiC and be compatible with current device fabrication.

CO2 Cluster Ion Beam, an Alternative Projectile for Secondary Ion Mass Spectrometry.

PubMed

Tian, Hua; Maciążek, Dawid; Postawa, Zbigniew; Garrison, Barbara J; Winograd, Nicholas

2016-09-01

The emergence of argon-based gas cluster ion beams for SIMS experiments opens new possibilities for molecular depth profiling and 3D chemical imaging. These beams generally leave less surface chemical damage and yield mass spectra with reduced fragmentation compared with smaller cluster projectiles. For nanoscale bioimaging applications, however, limited sensitivity due to low ionization probability and technical challenges of beam focusing remain problematic. The use of gas cluster ion beams based upon systems other than argon offer an opportunity to resolve these difficulties. Here we report on the prospects of employing CO2 as a simple alternative to argon. Ionization efficiency, chemical damage, sputter rate, and beam focus are investigated on model compounds using a series of CO2 and Ar cluster projectiles (cluster size 1000-5000) with the same mass. The results show that the two projectiles are very similar in each of these aspects. Computer simulations comparing the impact of Ar2000 and (CO2)2000 on an organic target also confirm that the CO2 molecules in the cluster projectile remain intact, acting as a single particle of m/z 44. The imaging resolution employing CO2 cluster projectiles is improved by more than a factor of two. The advantage of CO2 versus Ar is also related to the increased stability which, in addition, facilitates the operation of the gas cluster ion beams (GCIB) system at lower backing pressure. Graphical Abstract ᅟ.

Growth Mechanism of Cluster-Assembled Surfaces: From Submonolayer to Thin-Film Regime

NASA Astrophysics Data System (ADS)

Borghi, Francesca; Podestà, Alessandro; Piazzoni, Claudio; Milani, Paolo

2018-04-01

Nanostructured films obtained by assembling preformed atomic clusters are of strategic importance for a wide variety of applications. The deposition of clusters produced in the gas phase onto a substrate offers the possibility to control and engineer the structural and functional properties of the cluster-assembled films. To date, the microscopic mechanisms underlying the growth and structuring of cluster-assembled films are poorly understood, and, in particular, the transition from the submonolayer to the thin-film regime is experimentally unexplored. Here we report the systematic characterization by atomic force microscopy of the evolution of the structural properties of cluster-assembled films deposited by supersonic cluster beam deposition. As a paradigm of nanostructured systems, we focus our attention on cluster-assembled zirconia films, investigating the influence of the building block dimensions on the growth mechanisms and roughening of the thin films, following the growth process from the early stages of the submonolayer to the thin-film regime. Our results demonstrate that the growth dynamics in the submonolayer regime determines different morphological properties of the cluster-assembled thin film. The evolution of the roughness with the number of deposited clusters reproduces the growth exponent of the ballistic deposition in the 2 +1 model from the submonolayer to the thin-film regime.

Optical Tweezers for Sample Fixing in Micro-Diffraction Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amenitsch, H.; Rappolt, M.; Sartori, B.

2007-01-19

In order to manipulate, characterize and measure the micro-diffraction of individual structural elements down to single phospholipid liposomes we have been using optical tweezers (OT) combined with an imaging microscope. We were able to install the OT system at the microfocus beamline ID13 at the ESRF and trap clusters of about 50 multi-lamellar liposomes (< 10 {mu}m large cluster). Further we have performed a scanning diffraction experiment with a 1 micrometer beam to demonstrate the fixing capabilities and to confirm the size of the liposome cluster by X-ray diffraction.

Metastability of the atomic structures of size-selected gold nanoparticles

NASA Astrophysics Data System (ADS)

Wells, Dawn M.; Rossi, Giulia; Ferrando, Riccardo; Palmer, Richard E.

2015-04-01

All nanostructures are metastable - but some are more metastable than others. Here we employ aberration-corrected electron microscopy and atomistic computer simulations to demonstrate the hierarchy of metastability in deposited, size-selected gold nanoparticles (clusters), an archetypal class of nanomaterials well known for the catalytic activity which only appears on the nanometer-scale. We show that the atomic structures presented by ``magic number'' Au561, Au742 and Au923 clusters are ``locked''. They are in fact determined by the solidification which occurs from the liquid state early in their growth (by assembly from atoms in the gas phase) followed by template growth. It is quite likely that transitions from a locked, metastable configuration to a more stable (but still metastable) structure, as observed here under the electron beam, will occur during catalytic reactions, for example.All nanostructures are metastable - but some are more metastable than others. Here we employ aberration-corrected electron microscopy and atomistic computer simulations to demonstrate the hierarchy of metastability in deposited, size-selected gold nanoparticles (clusters), an archetypal class of nanomaterials well known for the catalytic activity which only appears on the nanometer-scale. We show that the atomic structures presented by ``magic number'' Au561, Au742 and Au923 clusters are ``locked''. They are in fact determined by the solidification which occurs from the liquid state early in their growth (by assembly from atoms in the gas phase) followed by template growth. It is quite likely that transitions from a locked, metastable configuration to a more stable (but still metastable) structure, as observed here under the electron beam, will occur during catalytic reactions, for example. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05811a

Search for α-Cluster Structure in Exotic Nuclei with the Prototype Active-Target Time-Projection Chamber

NASA Astrophysics Data System (ADS)

Fritsch, A.; Ayyad, Y.; Bazin, D.; Beceiro-Novo, S.; Bradt, J.; Carpenter, L.; Cortesi, M.; Mittig, W.; Suzuki, D.; Ahn, T.; Kolata, J. J.; Becchetti, F. D.; Howard, A. M.

2016-03-01

Some exotic nuclei appear to exhibit α-cluster structure. While various theoretical models currently describe such clustering, more experimental data are needed to constrain model predictions. The Prototype Active-Target Time-Projection Chamber (PAT-TPC) has low-energy thresholds for charged-particle decay and a high luminosity due to its thick gaseous active target volume, making it well-suited to search for low-energy α-cluster reactions. Radioactive-ion beams produced by the TwinSol facility at the University of Notre Dame were delivered to the PAT-TPC to study nuclei including 14C and 14O via α-resonant scattering. Differential cross sections and excitation functions were measured. Preliminary results from our recent experiments will be presented. This work is supported by the U.S. National Science Foundation.

Elastic alpha-particle resonances as evidence of clustering at high excitation in 40Ca

NASA Astrophysics Data System (ADS)

Norrby, M.; Lönnroth, T.; Goldberg, V. Z.; Rogachev, G. V.; Golovkov, M. S.; Källman, K.-M.; Lattuada, M.; Perov, S. V.; Romano, S.; Skorodumov, B. B.; Tiourin, G. P.; Trzaska, W. H.; Tumino, A.; Vorontsov, A. N.

2011-08-01

The elastic-scattering reaction 36Ar + α was studied using the Thick Target Inverse Kinematics technique. Data were taken at a beam energy of 150 MeV in a reaction chamber filled with 4He gas, corresponding to the excitation region of 12-20 MeV in 40Ca. Using a simplified R -matrix method of analysis energies, widths and spin assignments were obtained for 137 resonances. The structure is discussed within the concept of α-cluster structure in the quasi-continuum of 40Ca and is compared to other nuclei in the same mass region.

Monoatomic and cluster beam effect on ToF-SIMS spectra of self-assembled monolayers on gold

NASA Astrophysics Data System (ADS)

Tuccitto, N.; Torrisi, V.; Delfanti, I.; Licciardello, A.

2008-12-01

Self-assembled monolayers represent well-defined systems that is a good model surface to study the effect of primary ion beams used in secondary ion mass spectrometry. The effect of polyatomic primary beams on both aliphatic and aromatic self-assembled monolayers has been studied. In particular, we analysed the variation of the relative secondary ion yield of both substrate metal-cluster (Au n-) in comparison with the molecular ions (M -) and clusters (M xAu y-) by using Bi +, Bi 3+, Bi 5+ beams. Moreover, the differences in the secondary ion generation efficiency are discussed. The main effect of the cluster beams is related to an increased formation of low-mass fragments and to the enhancement of the substrate related gold-clusters. The results show that, at variance of many other cases, the static SIMS of self-assembled monolayers does not benefit of the use of polyatomic primary ions.

Photofragment slice imaging studies of pyrrole and the Xe{center_dot}{center_dot}{center_dot}pyrrole cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubio-Lago, L.; Zaouris, D.; Sakellariou, Y.

The photolysis of pyrrole has been studied in a molecular beam at wavelengths of 250, 240, and 193.3 nm, using two different carrier gases, He and Xe. A broad bimodal distribution of H-atom fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm, sharp features have been observed in the fast part of the H-atom distribution. Under appropriate molecular beam conditions, the entire H-atom loss signal from the photolysis of pyrrole at both 240 and 250 nm (including the sharp features) disappear when using Xe as opposed to He as the carrier gas. Wemore » attribute this phenomenon to cluster formation between Xe and pyrrole, and this assumption is supported by the observation of resonance enhanced multiphoton ionization spectra for the (Xe{center_dot}{center_dot}{center_dot}pyrrole) cluster followed by photofragmentation of the nascent cation cluster. Ab initio calculations are presented for the ground states of the neutral and cationic (Xe{center_dot}{center_dot}{center_dot}pyrrole) clusters as a means of understanding their structural and energetic properties.« less

Computational Design of Clusters for Catalysis

NASA Astrophysics Data System (ADS)

Jimenez-Izal, Elisa; Alexandrova, Anastassia N.

2018-04-01

When small clusters are studied in chemical physics or physical chemistry, one perhaps thinks of the fundamental aspects of cluster electronic structure, or precision spectroscopy in ultracold molecular beams. However, small clusters are also of interest in catalysis, where the cold ground state or an isolated cluster may not even be the right starting point. Instead, the big question is: What happens to cluster-based catalysts under real conditions of catalysis, such as high temperature and coverage with reagents? Myriads of metastable cluster states become accessible, the entire system is dynamic, and catalysis may be driven by rare sites present only under those conditions. Activity, selectivity, and stability are highly dependent on size, composition, shape, support, and environment. To probe and master cluster catalysis, sophisticated tools are being developed for precision synthesis, operando measurements, and multiscale modeling. This review intends to tell the messy story of clusters in catalysis.

Weak gravitational lensing due to large-scale structure of the universe

NASA Technical Reports Server (NTRS)

Jaroszynski, Michal; Park, Changbom; Paczynski, Bohdan; Gott, J. Richard, III

1990-01-01

The effect of the large-scale structure of the universe on the propagation of light rays is studied. The development of the large-scale density fluctuations in the omega = 1 universe is calculated within the cold dark matter scenario using a smooth particle approximation. The propagation of about 10 to the 6th random light rays between the redshift z = 5 and the observer was followed. It is found that the effect of shear is negligible, and the amplification of single images is dominated by the matter in the beam. The spread of amplifications is very small. Therefore, the filled-beam approximation is very good for studies of strong lensing by galaxies or clusters of galaxies. In the simulation, the column density was averaged over a comoving area of approximately (1/h Mpc)-squared. No case of a strong gravitational lensing was found, i.e., no 'over-focused' image that would suggest that a few images might be present. Therefore, the large-scale structure of the universe as it is presently known does not produce multiple images with gravitational lensing on a scale larger than clusters of galaxies.

Richard E. Smalley, Buckminsterfullerene (the Buckyball), and Nanotubes

Science.gov Websites

: 723-730; July 1997 Supersonic Bare Metal Cluster Beams. Technical Progress Report, March 16, 1984  – April 1, 1985 Includes early cold ion beam technology research Supersonic Bare Metal Cluster Beams

NOTE: MMCTP: a radiotherapy research environment for Monte Carlo and patient-specific treatment planning

NASA Astrophysics Data System (ADS)

Alexander, A.; DeBlois, F.; Stroian, G.; Al-Yahya, K.; Heath, E.; Seuntjens, J.

2007-07-01

Radiotherapy research lacks a flexible computational research environment for Monte Carlo (MC) and patient-specific treatment planning. The purpose of this study was to develop a flexible software package on low-cost hardware with the aim of integrating new patient-specific treatment planning with MC dose calculations suitable for large-scale prospective and retrospective treatment planning studies. We designed the software package 'McGill Monte Carlo treatment planning' (MMCTP) for the research development of MC and patient-specific treatment planning. The MMCTP design consists of a graphical user interface (GUI), which runs on a simple workstation connected through standard secure-shell protocol to a cluster for lengthy MC calculations. Treatment planning information (e.g., images, structures, beam geometry properties and dose distributions) is converted into a convenient MMCTP local file storage format designated, the McGill RT format. MMCTP features include (a) DICOM_RT, RTOG and CADPlan CART format imports; (b) 2D and 3D visualization views for images, structure contours, and dose distributions; (c) contouring tools; (d) DVH analysis, and dose matrix comparison tools; (e) external beam editing; (f) MC transport calculation from beam source to patient geometry for photon and electron beams. The MC input files, which are prepared from the beam geometry properties and patient information (e.g., images and structure contours), are uploaded and run on a cluster using shell commands controlled from the MMCTP GUI. The visualization, dose matrix operation and DVH tools offer extensive options for plan analysis and comparison between MC plans and plans imported from commercial treatment planning systems. The MMCTP GUI provides a flexible research platform for the development of patient-specific MC treatment planning for photon and electron external beam radiation therapy. The impact of this tool lies in the fact that it allows for systematic, platform-independent, large-scale MC treatment planning for different treatment sites. Patient recalculations were performed to validate the software and ensure proper functionality.

Search for α -Cluster Structure in Exotic Nuclei with the Prototype Active-Target Time-Projection Chamber

NASA Astrophysics Data System (ADS)

Fritsch, A.; Ayyad, Y.; Bazin, D.; Beceiro-Novo, S.; Bradt, J.; Carpenter, L.; Cortesi, M.; Mittig, W.; Suzuki, D.; Ahn, T.; Kolata, J. J.; Howard, A. M.; Becchetti, F. D.; Wolff, M.

Some exotic nuclei appear to exhibit α -cluster structure, which may impact nucleosynthesis reaction rates. While various theoretical models currently describe such clustering, more experimental data are needed to constrain model predictions. The Prototype Active-Target Time-Projection Chamber (PAT-TPC) has low-energy thresholds for charged-particle decay and a high detection efficiency due to its thick gaseous active target volume, making it well-suited to search for low-energy α -cluster reactions. Radioactive-ion beams produced by the TwinSol facility at the University of Notre Dame were delivered to the PAT-TPC to study 14C via α -resonant scattering. Differential cross sections and excitation functions were measured and show evidence of three-body exit channels. Additional data were measured with an updated Micromegas detector more sensitive to three-body decay. Preliminary results are presented.

Method of precisely modifying predetermined surface layers of a workpiece by cluster ion impact therewith

DOEpatents

Friedman, L.; Beuhler, R.J.; Matthew, M.W.; Ledbetter, M.

1984-06-25

A method of precisely modifying a selected area of a workpiece by producing a beam of charged cluster ions that is narrowly mass selected to a predetermined mean size of cluster ions within a range of 25 to 10/sup 6/ atoms per cluster ion, and accelerated in a beam to a critical velocity. The accelerated beam is used to impact a selected area of an outer surface of the workpiece at a preselected rate of impacts of cluster ions/cm/sup 2//sec in order to effect a precise modification in that selected area of the workpiece.

Method of precisely modifying predetermined surface layers of a workpiece by cluster ion impact therewith

DOEpatents

Friedman, Lewis; Buehler, Robert J.; Matthew, Michael W.; Ledbetter, Myron

1985-01-01

A method of precisely modifying a selected area of a workpiece by producing a beam of charged cluster ions that is narrowly mass selected to a predetermined mean size of cluster ions within a range of 25 to 10.sup.6 atoms per cluster ion, and accelerated in a beam to a critical velocity. The accelerated beam is used to impact a selected area of an outer surface of the workpiece at a preselected rate of impacts of cluster ions/cm.sup.2 /sec. in order to effect a precise modification in that selected area of the workpiece.

Cluster-assembled metallic glasses

PubMed Central

2013-01-01

A bottom-up approach to nanofabricate metallic glasses from metal clusters as building blocks is presented. Considering metallic glasses as a subclass of cluster-assembled materials, the relation between the two lively fields of metal clusters and metallic glasses is pointed out. Deposition of selected clusters or collections of them, generated by state-of-the-art cluster beam sources, could lead to the production of a well-defined amorphous material. In contrast to rapidly quenched glasses where only the composition of the glass can be controlled, in cluster-assembled glasses, one can precisely control the structural building blocks. Comparing properties of glasses with similar compositions but differing in building blocks and therefore different in structure will facilitate the study of structure–property correlation in metallic glasses. This bottom-up method provides a novel alternative path to the synthesis of glassy alloys and will contribute to improving fundamental understanding in the field of metallic glasses. It may even permit the production of glassy materials for alloys that cannot be quenched rapidly enough to circumvent crystallization. Additionally, gaining deeper insight into the parameters governing the structure–property relation in metallic glasses can have a great impact on understanding and design of other cluster-assembled materials. PMID:23899019

Beam Design and User Scheduling for Nonorthogonal Multiple Access With Multiple Antennas Based on Pareto Optimality

NASA Astrophysics Data System (ADS)

Seo, Junyeong; Sung, Youngchul

2018-06-01

In this paper, an efficient transmit beam design and user scheduling method is proposed for multi-user (MU) multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) downlink, based on Pareto-optimality. The proposed beam design and user scheduling method groups simultaneously-served users into multiple clusters with practical two users in each cluster, and then applies spatical zeroforcing (ZF) across clusters to control inter-cluster interference (ICI) and Pareto-optimal beam design with successive interference cancellation (SIC) to two users in each cluster to remove interference to strong users and leverage signal-to-interference-plus-noise ratios (SINRs) of interference-experiencing weak users. The proposed method has flexibility to control the rates of strong and weak users and numerical results show that the proposed method yields good performance.

Importance of many-body dispersion and temperature effects on gas-phase gold cluster (meta)stability

NASA Astrophysics Data System (ADS)

Goldsmith, Bryan R.; Gruene, Philipp; Lyon, Jonathan T.; Rayner, David M.; Fielicke, André; Scheffler, Matthias; Ghiringhelli, Luca M.

Gold clusters in the gas phase exhibit many structural isomers that are shown to intercovert frequently, even at room temperature. We performed ab initio replica-exchange molecular dynamics (REMD) calculations on gold clusters (of sizes 5-14 atoms) to identify metastable states and their relative populations at finite temperature, as well as to examine the importance of temperature and van der Waals (vdW) on their isomer energetic ordering. Free energies of the gold cluster isomers are optimally estimated using the Multistate Bennett Acceptance Ratio. The distribution of bond coordination numbers and radius of gyration are used to address the challenge of discriminating isomers along their dynamical trajectories. Dispersion effects are important for stabilizing three-dimensional structures relative to planar structures and brings isomer energetic predictions to closer quantitative agreement compared with RPA@PBE calculations. We find that higher temperatures typically stabilize metastable three-dimensional structures relative to planar/quasiplanar structures. Computed IR spectra of low free energy Au9, Au10, and Au12 isomers are in agreement with experimental spectra obtained by far-IR multiple photon dissociation in a molecular beam at 100 K.

Structure, Bonding and Surface Chemistry of Metal Oxide Nanoclusters

DTIC Science & Technology

2015-06-23

studies to cobalt and chromium oxides and to both oxides and pure metal clusters of aluminum, using acetonitrile as the ligand. The chromium solutions...seen in molecular beam experiments. The cobalt oxide sample produced a blue solution, and mass spectra had a single main peak at 551 amu. Mass...of cobalt and nickel oxide cluster cations," J. Phys. Chem. A 116, 5398-5404 (2012). DOI: 10.1021/jp302560p. 4. A. M. Ricks, A. D. Brathwaite, M

Development of Metal Cluster-Based Energetic Materials at NSWC-IHD

DTIC Science & Technology

2011-01-01

reactivity of NixAly + clusters with nitromethane was investigated using a gas-phase molecular beam system. Results indicate that nitromethane is highly...clusters make up the subunit of a molecular metal-based energetic material. The reactivity of NixAly+ clusters with nitromethane was investigated using...a gas-phase molecular beam system. Results indicate that nitromethane is highly reactive toward the NixAly+ clusters and suggests it would not make

Vlasov Simulation of Electrostatic Solitary Structures in Multi-Component Plasmas

NASA Technical Reports Server (NTRS)

Umeda, Takayuki; Ashour-Abdalla, Maha; Pickett, Jolene S.; Goldstein, Melvyn L.

2012-01-01

Electrostatic solitary structures have been observed in the Earth's magnetosheath by the Cluster spacecraft. Recent theoretical work has suggested that these solitary structures are modeled by electron acoustic solitary waves existing in a four-component plasma system consisting of core electrons, two counter-streaming electron beams, and one species of background ions. In this paper, the excitation of electron acoustic waves and the formation of solitary structures are studied by means of a one-dimensional electrostatic Vlasov simulation. The present result first shows that either electron acoustic solitary waves with negative potential or electron phase-space holes with positive potential are excited in four-component plasma systems. However, these electrostatic solitary structures have longer duration times and higher wave amplitudes than the solitary structures observed in the magnetosheath. The result indicates that a high-speed and small free energy source may be needed as a fifth component. An additional simulation of a five-component plasma consisting of a stable four-component plasma and a weak electron beam shows the generation of small and fast electron phase-space holes by the bump-on-tail instability. The physical properties of the small and fast electron phase-space holes are very similar to those obtained by the previous theoretical analysis. The amplitude and duration time of solitary structures in the simulation are also in agreement with the Cluster observation.

Investigation of Damage with Cluster Ion Beam Irradiation Using HR-RBS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seki, Toshio; Aoki, Takaaki; Matsuo, Jiro

2008-11-03

Cluster ion beam can process targets with shallow damage because of the very low irradiation energy per atom. However, it is needed to investigate the damage with cluster ion beam irradiation, because recent applications demand process targets with ultra low damage. The shallow damage can be investigated from depth profiles of specific species before and after ion irradiation. They can be measured with secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectroscopy (RBS). High resolution Rutherford backscattering spectroscopy (HR-RBS) is a non destructive measurement method and depth profiles can be measured with nano-resolution. The cluster ion beam mixing of thinmore » Ni layer in carbon targets can be investigated with HR-RBS. The mixing depth with cluster ion irradiation at 10 keV was about 10 nm. The mixing depth with cluster ion irradiation at 1 keV and 5 keV were less than 1 nm and 5 nm, respectively. The number of displaced Ni atoms with cluster ion irradiation was very larger than that with monomer ion irradiation of same energy. This result shows that violent mixing occurs with single cluster impact.« less

Far-infrared spectra of yttrium-doped gold clusters Au(n)Y (n=1-9).

PubMed

Lin, Ling; Claes, Pieterjan; Gruene, Philipp; Meijer, Gerard; Fielicke, André; Nguyen, Minh Tho; Lievens, Peter

2010-06-21

The geometric, spectroscopic, and electronic properties of neutral yttrium-doped gold clusters Au(n)Y (n=1-9) are studied by far-infrared multiple photon dissociation (FIR-MPD) spectroscopy and quantum chemical calculations. Comparison of the observed and calculated vibrational spectra allows the structures of the isomers present in the molecular beam to be determined. Most of the isomers for which the IR spectra agree best with experiment are calculated to be the energetically most stable ones. Attachment of xenon to the Au(n)Y cluster can cause changes in the IR spectra, which involve band shifts and band splittings. In some cases symmetry changes, as a result of the attachment of xenon atoms, were also observed. All the Au(n)Y clusters considered prefer a low spin state. In contrast to pure gold clusters, which exhibit exclusively planar lowest-energy structures for small sizes, several of the studied species are three-dimensional. This is particularly the case for Au(4)Y and Au(9)Y, while for some other sizes (n=5, 8) the 3D structures have an energy similar to that of their 2D counterparts. Several of the lowest-energy structures are quasi-2D, that is, slightly distorted from planar shapes. For all the studied species the Y atom prefers high coordination, which is different from other metal dopants in gold clusters.

Defect Clustering and Nano-Phase Structure Characterization of Multi-Component Rare Earth Oxide Doped Zirconia-Yttria Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Chen, Yuan L.; Miller, Robert A.

2003-01-01

Advanced oxide thermal barrier coatings have been developed by incorporating multi-component rare earth oxide dopants into zirconia-yttria to effectively promote the creation of the thermodynamically stable, immobile oxide defect clusters and/or nano-scale phases within the coating systems. The presence of these nano-sized defect clusters has found to significantly reduce the coating intrinsic thermal conductivity, improve sintering resistance, and maintain long-term high temperature stability. In this paper, the defect clusters and nano-structured phases, which were created by the addition of multi-component rare earth dopants to the plasma-sprayed and electron-beam physical vapor deposited thermal barrier coatings, were characterized by high-resolution transmission electron microscopy (TEM). The defect cluster size, distribution, crystallographic and compositional information were investigated using high-resolution TEM lattice imaging, selected area diffraction (SAD), electron energy-loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) analysis techniques. The results showed that substantial defect clusters were formed in the advanced multi-component rare earth oxide doped zirconia- yttria systems. The size of the oxide defect clusters and the cluster dopant segregation was typically ranging from 5 to 50 nm. These multi-component dopant induced defect clusters are an important factor for the coating long-term high temperature stability and excellent performance.

Defect Clustering and Nano-Phase Structure Characterization of Multi-Component Rare Earth Oxide Doped Zirconia-Yttria Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Chen, Yuan L.; Miller, Robert A.

1990-01-01

Advanced oxide thermal barrier coatings have been developed by incorporating multi- component rare earth oxide dopants into zirconia-yttria to effectively promote the creation of the thermodynamically stable, immobile oxide defect clusters and/or nano-scale phases within the coating systems. The presence of these nano-sized defect clusters has found to significantly reduce the coating intrinsic thermal conductivity, improve sintering resistance, and maintain long-term high temperature stability. In this paper, the defect clusters and nano-structured phases, which were created by the addition of multi-component rare earth dopants to the plasma- sprayed and electron-beam physical vapor deposited thermal barrier coatings, were characterized by high-resolution transmission electron microscopy (TEM). The defect cluster size, distribution, crystallographic and compositional information were investigated using high-resolution TEM lattice imaging, selected area diffraction (SAD), and energy dispersive spectroscopy (EDS) analysis techniques. The results showed that substantial defect clusters were formed in the advanced multi-component rare earth oxide doped zirconia-yttria systems. The size of the oxide defect clusters and the cluster dopant segregation was typically ranging fiom 5 to 50 nm. These multi-component dopant induced defect clusters are an important factor for the coating long-term high temperature stability and excellent performance.

The Existence of a Designer Al=Al Double Bond in the LiAl2 H4- Cluster Formed by Electronic Transmutation.

PubMed

Lundell, Katie A; Zhang, Xinxing; Boldyrev, Alexander I; Bowen, Kit H

2017-12-22

The Al=Al double bond is elusive in chemistry. Herein we report the results obtained via combined photoelectron spectroscopy and ab initio studies of the LiAl 2 H 4 - cluster that confirm the formation of a conventional Al=Al double bond. Comprehensive searches for the most stable structures of the LiAl 2 H 4 - cluster have shown that the global minimum isomer I possesses a geometric structure which resembles that of Si 2 H 4 , demonstrating a successful example of the transmutation of Al atoms into Si atoms by electron donation. Theoretical simulations of the photoelectron spectrum discovered the coexistence of two isomers in the ion beam, including the one with the Al=Al double bond. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of isolated and clustered DNA damage and the post-irradiating repair process in the effects of heavy ion beam irradiation.

PubMed

Tokuyama, Yuka; Furusawa, Yoshiya; Ide, Hiroshi; Yasui, Akira; Terato, Hiroaki

2015-05-01

Clustered DNA damage is a specific type of DNA damage induced by ionizing radiation. Any type of ionizing radiation traverses the target DNA molecule as a beam, inducing damage along its track. Our previous study showed that clustered DNA damage yields decreased with increased linear energy transfer (LET), leading us to investigate the importance of clustered DNA damage in the biological effects of heavy ion beam radiation. In this study, we analyzed the yield of clustered base damage (comprising multiple base lesions) in cultured cells irradiated with various heavy ion beams, and investigated isolated base damage and the repair process in post-irradiation cultured cells. Chinese hamster ovary (CHO) cells were irradiated by carbon, silicon, argon and iron ion beams with LETs of 13, 55, 90 and 200 keV µm(-1), respectively. Agarose gel electrophoresis of the cells with enzymatic treatments indicated that clustered base damage yields decreased as the LET increased. The aldehyde reactive probe procedure showed that isolated base damage yields in the irradiated cells followed the same pattern. To analyze the cellular base damage process, clustered DNA damage repair was investigated using DNA repair mutant cells. DNA double-strand breaks accumulated in CHO mutant cells lacking Xrcc1 after irradiation, and the cell viability decreased. On the other hand, mouse embryonic fibroblast (Mef) cells lacking both Nth1 and Ogg1 became more resistant than the wild type Mef. Thus, clustered base damage seems to be involved in the expression of heavy ion beam biological effects via the repair process. © The Author 2015. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

The quantitative analysis of silicon carbide surface smoothing by Ar and Xe cluster ions

NASA Astrophysics Data System (ADS)

Ieshkin, A. E.; Kireev, D. S.; Ermakov, Yu. A.; Trifonov, A. S.; Presnov, D. E.; Garshev, A. V.; Anufriev, Yu. V.; Prokhorova, I. G.; Krupenin, V. A.; Chernysh, V. S.

2018-04-01

The gas cluster ion beam technique was used for the silicon carbide crystal surface smoothing. The effect of processing by two inert cluster ions, argon and xenon, was quantitatively compared. While argon is a standard element for GCIB, results for xenon clusters were not reported yet. Scanning probe microscopy and high resolution transmission electron microscopy techniques were used for the analysis of the surface roughness and surface crystal layer quality. The gas cluster ion beam processing results in surface relief smoothing down to average roughness about 1 nm for both elements. It was shown that xenon as the working gas is more effective: sputtering rate for xenon clusters is 2.5 times higher than for argon at the same beam energy. High resolution transmission electron microscopy analysis of the surface defect layer gives values of 7 ± 2 nm and 8 ± 2 nm for treatment with argon and xenon clusters.

High-resolution simulation of deep pencil beam surveys - analysis of quasi-periodicity

NASA Astrophysics Data System (ADS)

Weiss, A. G.; Buchert, T.

1993-07-01

We carry out pencil beam constructions in a high-resolution simulation of the large-scale structure of galaxies. The initial density fluctuations are taken to have a truncated power spectrum. All the models have {OMEGA} = 1. As an example we present the results for the case of "Hot-Dark-Matter" (HDM) initial conditions with scale-free n = 1 power index on large scales as a representative of models with sufficient large-scale power. We use an analytic approximation for particle trajectories of a self-gravitating dust continuum and apply a local dynamical biasing of volume elements to identify luminous matter in the model. Using this method, we are able to resolve formally a simulation box of 1200h^-1^ Mpc (e.g. for HDM initial conditions) down to the scale of galactic halos using 2160^3^ particles. We consider this as the minimal resolution necessary for a sensible simulation of deep pencil beam data. Pencil beam probes are taken for a given epoch using the parameters of observed beams. In particular, our analysis concentrates on the detection of a quasi-periodicity in the beam probes using several different methods. The resulting beam ensembles are analyzed statistically using number distributions, pair-count histograms, unnormalized pair-counts, power spectrum analysis and trial-period folding. Periodicities are classified according to their significance level in the power spectrum of the beams. The simulation is designed for application to parameter studies which prepare future observational projects. We find that a large percentage of the beams show quasi- periodicities with periods which cluster at a certain length scale. The periods found range between one and eight times the cutoff length in the initial fluctuation spectrum. At significance levels similar to those of the data of Broadhurst et al. (1990), we find about 15% of the pencil beams to show periodicities, about 30% of which are around the mean separation of rich clusters, while the distribution of scales reaches values of more than 200h^-1^ Mpc. The detection of periodicities larger than the typical void size must not be due to missing of "walls" (like the so called "Great Wall" seen in the CfA catalogue of galaxies), but can be due to different clustering properties of galaxies along the beams.

Water cluster fragmentation probed by pickup experiments

NASA Astrophysics Data System (ADS)

Huang, Chuanfu; Kresin, Vitaly V.; Pysanenko, Andriy; Fárník, Michal

2016-09-01

Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ˜3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics.

Loss of balance during balance beam walking elicits a multifocal theta band electrocortical response

PubMed Central

Gwin, Joseph T.; Makeig, Scott; Ferris, Daniel P.

2013-01-01

Determining the neural correlates of loss of balance during walking could lead to improved clinical assessment and treatment for individuals predisposed to falls. We used high-density electroencephalography (EEG) combined with independent component analysis (ICA) to study loss of balance during human walking. We examined 26 healthy young subjects performing heel-to-toe walking on a treadmill-mounted balance beam as well as walking on the treadmill belt (both at 0.22 m/s). ICA identified clusters of electrocortical EEG sources located in or near anterior cingulate, anterior parietal, superior dorsolateral-prefrontal, and medial sensorimotor cortex that exhibited significantly larger mean spectral power in the theta band (4–7 Hz) during walking on the balance beam compared with treadmill walking. Left and right sensorimotor cortex clusters produced significantly less power in the beta band (12–30 Hz) during walking on the balance beam compared with treadmill walking. For each source cluster, we also computed a normalized mean time/frequency spectrogram time locked to the gait cycle during loss of balance (i.e., when subjects stepped off the balance beam). All clusters except the medial sensorimotor cluster exhibited a transient increase in theta band power during loss of balance. Cluster spectrograms demonstrated that the first electrocortical indication of impending loss of balance occurred in the left sensorimotor cortex at the transition from single support to double support prior to stepping off the beam. These findings provide new insight into the neural correlates of walking balance control and could aid future studies on elderly individuals and others with balance impairments. PMID:23926037

Loss of balance during balance beam walking elicits a multifocal theta band electrocortical response.

PubMed

Sipp, Amy R; Gwin, Joseph T; Makeig, Scott; Ferris, Daniel P

2013-11-01

Determining the neural correlates of loss of balance during walking could lead to improved clinical assessment and treatment for individuals predisposed to falls. We used high-density electroencephalography (EEG) combined with independent component analysis (ICA) to study loss of balance during human walking. We examined 26 healthy young subjects performing heel-to-toe walking on a treadmill-mounted balance beam as well as walking on the treadmill belt (both at 0.22 m/s). ICA identified clusters of electrocortical EEG sources located in or near anterior cingulate, anterior parietal, superior dorsolateral-prefrontal, and medial sensorimotor cortex that exhibited significantly larger mean spectral power in the theta band (4-7 Hz) during walking on the balance beam compared with treadmill walking. Left and right sensorimotor cortex clusters produced significantly less power in the beta band (12-30 Hz) during walking on the balance beam compared with treadmill walking. For each source cluster, we also computed a normalized mean time/frequency spectrogram time locked to the gait cycle during loss of balance (i.e., when subjects stepped off the balance beam). All clusters except the medial sensorimotor cluster exhibited a transient increase in theta band power during loss of balance. Cluster spectrograms demonstrated that the first electrocortical indication of impending loss of balance occurred in the left sensorimotor cortex at the transition from single support to double support prior to stepping off the beam. These findings provide new insight into the neural correlates of walking balance control and could aid future studies on elderly individuals and others with balance impairments.

Beam production of 18Ne with in-flight method for alpha scattering at CRIB

NASA Astrophysics Data System (ADS)

Duy, N. N.; Chae, K. Y.; Cha, S. M.; Yamaguchi, H.; Abe, K.; Bae, S. H.; Binh, D. N.; Choi, S. H.; Hahn, K. I.; Hayakawa, S.; Hong, B.; Iwasa, N.; Kahl, D.; Khiem, L. H.; Kim, A.; Kim, D. H.; Kim, E. J.; Kim, G. W.; Kim, M. J.; Kwak, K.; Kwag, M. S.; Lee, E. J.; Lim, S. I.; Moon, B.; Moon, J. Y.; Park, S. Y.; Phong, V. H.; Shimizu, H.; Yang, L.; Ge, Z.; Hao, T. V. Nhan

2018-07-01

We conducted a measurement of 18Ne + α scattering in inverse kinematics, in order to search for experimental evidence of α-cluster structure in 22Mg above the alpha threshold (Ethr = 8 . 14 MeV) and determine the astrophysical rates of the 18Ne(α, p)21Na reaction under the conditions of break-out from the Hot-CNO cycle. A high intensity 18Ne beam at 2.54 AMeV was successfully produced at CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo. This paper presents the in-flight production of the radioactive 18Ne beam by using the production reaction 3He(16O, 18Ne)n with a windowed cryogenic gas target, which was employed in the mentioned resonant α-scattering experiment.

Damage and annealing recovery of boron-implanted ultra-shallow junction: The correlation between beam current and surface configuration

NASA Astrophysics Data System (ADS)

Chang, Feng-Ming; Wu, Zong-Zhe; Lin, Yen-Fu; Kao, Li-Chi; Wu, Cheng-Ta; JangJian, Shiu-Ko; Chen, Yuan-Nian; Lo, Kuang Yao

2018-03-01

The condition of the beam current in the implantation process is a key issue in the damage rate and structural evolution in the sequent annealing process, especially for ultra-shallow layers. In this work, we develop a compensative optical method combined with UV Raman, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge spectroscopy (XANES) to inspect the influence of the beam current in the implantation process. The optima condition of the beam current in the implantation process is determined by higher effective Si-B bond portion in UV Raman spectra and less the peak of B-B bond in XPS spectra which is caused by B cluster defects. Results of XANES indicate that the B oxide layer is formed on the surface of the ultra-shallow junction. The defects in the ultra-shallow junction after annealing are analyzed by novel optical analyses, which cannot be inspected by a traditional thermal wave and resistance measurement. This work exhibits the structural variation of the ultra-shallow junction via a variant beam current and provides a valuable metrology in examining the chemical states and the effective activation in the implantation technology.

FAST TRACK COMMUNICATION: Poly(methyl methacrylate)-palladium clusters nanocomposite formation by supersonic cluster beam deposition: a method for microstructured metallization of polymer surfaces

NASA Astrophysics Data System (ADS)

Ravagnan, Luca; Divitini, Giorgio; Rebasti, Sara; Marelli, Mattia; Piseri, Paolo; Milani, Paolo

2009-04-01

Nanocomposite films were fabricated by supersonic cluster beam deposition (SCBD) of palladium clusters on poly(methyl methacrylate) (PMMA) surfaces. The evolution of the electrical conductance with cluster coverage and microscopy analysis show that Pd clusters are implanted in the polymer and form a continuous layer extending for several tens of nanometres beneath the polymer surface. This allows the deposition, using stencil masks, of cluster-assembled Pd microstructures on PMMA showing a remarkably high adhesion compared with metallic films obtained by thermal evaporation. These results suggest that SCBD is a promising tool for the fabrication of metallic microstructures on flexible polymeric substrates.

Cluster Beam Studies.

DTIC Science & Technology

1988-04-01

Continue on reverse if necessary and identify by block number) Cluster beams offer a means of depositing high-quality thin films at low...either directly inclustered vapors of nonvolatile materials or Indirectly by bombarding the film duringdeposition with clusters of inert gases. When a...electron volt energy per atom. The suprathermal energy of thej depositing atoms is thought to produce unique thin films (either in quality, or in the ability

Structural analysis of the outermost hair surface using TOF-SIMS with gas cluster ion beam sputtering.

PubMed

Lshikawa, Kazutaka; Okamoto, Masayuki; Aoyagi, Satoka

2016-06-28

A hair cuticle, which consists of flat overlapping scales that surround the hair fiber, protects inner tissues against external stimuli. The outermost surface of the cuticle is covered with a thin membrane containing proteins and lipids called the epicuticle. In a previous study, the authors conducted a depth profile analysis of a hair cuticle's amino acid composition to characterize its multilayer structure. Time-of-flight secondary ion mass spectrometry with a bismuth primary ion source was used in combination with the C60 sputtering technique for the analysis. It was confirmed that the lipids and cysteine-rich layer exist on the outermost cuticle surface, which is considered to be the epicuticle, though the detailed structure of the epicuticle has not been clarified. In this study, depth profile analysis of the cuticle surface was conducted using the argon gas cluster ion beam (Ar-GCIB) sputtering technique, in order to characterize the structure of the epicuticle. The shallow depth profile of the cuticle surface was investigated using an Ar-GCIB impact energy of 5 keV. Compared to the other amino acid peaks rich in the epicuticle, the decay of 18-methyleicosanic acid (18-MEA) thiolate peak was the fastest. This result suggests that the outermost surface of the hair is rich in 18-MEA. In conclusion, our results indicate that the outermost surfaces of cuticles have a multilayer (lipid and protein layers), which is consistent with the previously proposed structure.

Bottom-up strategies for the assembling of magnetic systems using nanoclusters

NASA Astrophysics Data System (ADS)

Dupuis, V.; Hillion, A.; Robert, A.; Loiselet, O.; Khadra, G.; Capiod, P.; Albin, C.; Boisron, O.; Le Roy, D.; Bardotti, L.; Tournus, F.; Tamion, A.

2018-05-01

In the frame of the 20th Anniversary of the Journal of Nanoparticle Research (JNR), our aim is to start from the historical context 20 years ago and to give some recent results and perspectives concerning nanomagnets prepared from clusters preformed in the gas phase using the low-energy cluster beam deposition (LECBD) technique. In this paper, we focus our attention on the typical case of Co clusters embedded in various matrices to study interface magnetic anisotropy and magnetic interactions as a function of volume concentrations, and on still current and perspectives through two examples of binary metallic 3d-5d TM (namely CoPt and FeAu) cluster assemblies to illustrate size-related and nanoalloy phenomena on magnetic properties in well-defined mass-selected clusters. The structural and magnetic properties of these cluster assemblies were investigated using various experimental techniques that include high-resolution transmission electron microscopy (HRTEM), superconducting quantum interference device (SQUID) magnetometry, and synchrotron techniques such as extended X-ray absorption fine structure (EXAFS) and X-ray magnetic circular dichroism (XMCD). Depending on the chemical nature of both NPs and matrix, we observe different magnetic responses compared to their bulk counterparts. In particular, we show how finite size effects (size reduction) enhance their magnetic moment and how specific relaxation in nanoalloys can impact their magnetic anisotropy.

Infrared Multiple Photon Dissociation Spectroscopy Of Metal Cluster-Adducts

NASA Astrophysics Data System (ADS)

Cox, D. M.; Kaldor, A.; Zakin, M. R.

1987-01-01

Recent development of the laser vaporization technique combined with mass-selective detection has made possible new studies of the fundamental chemical and physical properties of unsupported transition metal clusters as a function of the number of constituent atoms. A variety of experimental techniques have been developed in our laboratory to measure ionization threshold energies, magnetic moments, and gas phase reactivity of clusters. However, studies have so far been unable to determine the cluster structure or the chemical state of chemisorbed species on gas phase clusters. The application of infrared multiple photon dissociation IRMPD to obtain the IR absorption properties of metal cluster-adsorbate species in a molecular beam is described here. Specifically using a high power, pulsed CO2 laser as the infrared source, the IRMPD spectrum for methanol chemisorbed on small iron clusters is measured as a function of the number of both iron atoms and methanols in the complex for different methanol isotopes. Both the feasibility and potential utility of IRMPD for characterizing metal cluster-adsorbate interactions are demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only upon the availability of appropriate high power infrared sources.

PREFACE: Nuclear Cluster Conference; Cluster'07

NASA Astrophysics Data System (ADS)

Freer, Martin

2008-05-01

The Cluster Conference is a long-running conference series dating back to the 1960's, the first being initiated by Wildermuth in Bochum, Germany, in 1969. The most recent meeting was held in Nara, Japan, in 2003, and in 2007 the 9th Cluster Conference was held in Stratford-upon-Avon, UK. As the name suggests the town of Stratford lies upon the River Avon, and shortly before the conference, due to unprecedented rainfall in the area (approximately 10 cm within half a day), lay in the River Avon! Stratford is the birthplace of the `Bard of Avon' William Shakespeare, and this formed an intriguing conference backdrop. The meeting was attended by some 90 delegates and the programme contained 65 70 oral presentations, and was opened by a historical perspective presented by Professor Brink (Oxford) and closed by Professor Horiuchi (RCNP) with an overview of the conference and future perspectives. In between, the conference covered aspects of clustering in exotic nuclei (both neutron and proton-rich), molecular structures in which valence neutrons are exchanged between cluster cores, condensates in nuclei, neutron-clusters, superheavy nuclei, clusters in nuclear astrophysical processes and exotic cluster decays such as 2p and ternary cluster decay. The field of nuclear clustering has become strongly influenced by the physics of radioactive beam facilities (reflected in the programme), and by the excitement that clustering may have an important impact on the structure of nuclei at the neutron drip-line. It was clear that since Nara the field had progressed substantially and that new themes had emerged and others had crystallized. Two particular topics resonated strongly condensates and nuclear molecules. These topics are thus likely to be central in the next cluster conference which will be held in 2011 in the Hungarian city of Debrechen. Martin Freer Participants and Cluster'07

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

PubMed Central

Golan, Amir; Ahmed, Musahid

2012-01-01

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9. We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3. PMID:23149375

Winds from the S-Star Cluster Reduce the Accretion Rate onto Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, Farhad; Wardle, M.; Roberts, D. A; Haggard, Daryl; Lacy, John H.; Royster, Marc; Cotton, William D.

2014-06-01

High-resolution radio continuum images of the region within a few arcseconds of Sgr A* at wavelengths of 7 and 12 mm show three new radio structures. One is a 2-3'' hollow teardrop-shaped structure centered on Sgr A*. Highly blue-shifted [NeII] and [FeIII] line emission is detected along the boundary of this teardrop-shaped bubble, ~2.2'' south of Sgr A*. The second structure is a faint, incomplete ring surrounding Sgr A* with typical surface brightness at 7 mm of ~0.1 mJy per ~0.04'' x 0.08'' beam. This partial ring coincides with the outer boundary of the S-star cluster which consists of ~30 B dwarfs orbiting within 1'' of Sgr A*. Lastly, on a scale of ~20'' to the N of Sgr A*, a balloon-shaped structure is detected.We interpret that the new morphological and kinematic structures result from the dynamical effects of a combined cluster wind. This wind is created at a rate ~3 x 10^{-5} solar mass per year by the merging of individual stellar winds from the B stars in the S-star cluster. What is significant about this interpretation is that the expanding wind excludes the shocked winds from O and WR stars in the central parsec of the Galaxy. Meanwhile Sgr A* accretes material from within the S cluster at a rate less than or equal 3 x 10^{-7} solar mass per year, thus explaining the low luminosity of Sgr A* without the ejection of a large fraction of the accreted material.

Development of Wien filter for small ion gun of surface analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bahng, Jungbae; Busan Center, Korea Basic Science Institute, Busan 609-735; Hong, Jonggi

The gas cluster ion beam (GCIB) and liquid metal ion beam have been studied in the context of ion beam usage for analytical equipment in applications such as X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS). In particular, small ion sources are used for the secondary ion generation and ion etching. To set the context to this study, the SIMS project has been launched to develop ion-gun based analytical equipment for the Korea Basic Science Institute. The objective of the first stage of the project is the generation of argon beams with a GCIB system [A. Kirkpatrick, Nucl. Instrum.more » Methods Phys. Res., Sect. B 206, 830–837 (2003)] that consists of a nozzle, skimmer, ionizer, acceleration tube, separation system, transport system, and target. The Wien filter directs the selected cluster beam to the target system by exploiting the velocity difference of the generated particles from GCIB. In this paper, we present the theoretical modeling and three-dimensional electromagnetic analysis of the Wien filter, which can separate Ar{sup +}{sub 2500} clusters from Ar{sup +}{sub 2400} to Ar{sup +}{sub 2600} clusters with a 1-mm collimator.« less

N-body simulations of gravitational redshifts and other relativistic distortions of galaxy clustering

NASA Astrophysics Data System (ADS)

Zhu, Hongyu; Alam, Shadab; Croft, Rupert A. C.; Ho, Shirley; Giusarma, Elena

2017-10-01

Large redshift surveys of galaxies and clusters are providing the first opportunities to search for distortions in the observed pattern of large-scale structure due to such effects as gravitational redshift. We focus on non-linear scales and apply a quasi-Newtonian approach using N-body simulations to predict the small asymmetries in the cross-correlation function of two galaxy different populations. Following recent work by Bonvin et al., Zhao and Peacock and Kaiser on galaxy clusters, we include effects which enter at the same order as gravitational redshift: the transverse Doppler effect, light-cone effects, relativistic beaming, luminosity distance perturbation and wide-angle effects. We find that all these effects cause asymmetries in the cross-correlation functions. Quantifying these asymmetries, we find that the total effect is dominated by the gravitational redshift and luminosity distance perturbation at small and large scales, respectively. By adding additional subresolution modelling of galaxy structure to the large-scale structure information, we find that the signal is significantly increased, indicating that structure on the smallest scales is important and should be included. We report on comparison of our simulation results with measurements from the SDSS/BOSS galaxy redshift survey in a companion paper.

Portable ultrahigh-vacuum sample storage system for polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Yoshihide, E-mail: e0827@mosk.tytlabs.co.jp; Nishimura, Yusaku F.; Suzuki, Ryo

A portable ultrahigh-vacuum sample storage system was designed and built to investigate the detailed geometric structures of mass-selected metal clusters on oxide substrates by polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy (PTRF-XAFS). This ultrahigh-vacuum (UHV) sample storage system provides the handover of samples between two different sample manipulating systems. The sample storage system is adaptable for public transportation, facilitating experiments using air-sensitive samples in synchrotron radiation or other quantum beam facilities. The samples were transferred by the developed portable UHV transfer system via a public transportation at a distance over 400 km. The performance of the transfer system was demonstratedmore » by a successful PTRF-XAFS study of Pt{sub 4} clusters deposited on a TiO{sub 2}(110) surface.« less

A new analysis technique to measure fusion excitation functions with large beam energy dispersions

NASA Astrophysics Data System (ADS)

Figuera, P.; Di Pietro, A.; Fisichella, M.; Lattuada, M.; Shotter, A. C.; Ruiz, C.; Zadro, M.

2018-01-01

Peculiar nuclear structures of two colliding nuclei such has clustering, neutron halo/skin or very low breakup thresholds can affect the reaction dynamics below the Coulomb barrier and this may also have astrophysical consequences. In order to have a better understanding of this topic, in the last decade, several experiments were performed. A typical experimental challenge of such studies is the need to measure excitation functions below the Coulomb barrier, having a strong energy dependence, with rather large beam energy dispersions inside the target. This may easily lead to ambiguities in associating the measured cross section with a proper beam energy. In this paper a discussion on this topic is reported and a new technique to deal with the above problem will be proposed.

Rhenium ion beam for implantation into semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulevoy, T. V.; Seleznev, D. N.; Alyoshin, M. E.

2012-02-15

At the ion source test bench in Institute for Theoretical and Experimental Physics the program of ion source development for semiconductor industry is in progress. In framework of the program the Metal Vapor Vacuum Arc ion source for germanium and rhenium ion beam generation was developed and investigated. It was shown that at special conditions of ion beam implantation it is possible to fabricate not only homogenous layers of rhenium silicides solid solutions but also clusters of this compound with properties of quantum dots. At the present moment the compound is very interesting for semiconductor industry, especially for nanoelectronics andmore » nanophotonics, but there is no very developed technology for production of nanostructures (for example quantum sized structures) with required parameters. The results of materials synthesis and exploration are presented.« less

Heterogeneous atmospheric chemistry

NASA Technical Reports Server (NTRS)

Schryer, D. R.

1982-01-01

The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.

Retrieval of Urban Boundary Layer Structures from Doppler Lidar Data. Part I: Accuracy Assessment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Quanxin; Lin, Ching Long; Calhoun, Ron

2008-01-01

Two coherent Doppler lidars from the US Army Research Laboratory (ARL) and Arizona State University (ASU) were deployed in the Joint Urban 2003 atmospheric dispersion field experiment (JU2003) held in Oklahoma City. The dual lidar data are used to evaluate the accuracy of the four-dimensional variational data assimilation (4DVAR) method and identify the coherent flow structures in the urban boundary layer. The objectives of the study are three-fold. The first objective is to examine the effect of eddy viscosity models on the quality of retrieved velocity data. The second objective is to determine the fidelity of single-lidar 4DVAR and evaluatemore » the difference between single- and dual-lidar retrievals. The third objective is to correlate the retrieved flow structures with the ground building data. It is found that the approach of treating eddy viscosity as part of control variables yields better results than the approach of prescribing viscosity. The ARL single-lidar 4DVAR is able to retrieve radial velocity fields with an accuracy of 98% in the along-beam direction and 80-90% in the cross-beam direction. For the dual-lidar 4DVAR, the accuracy of retrieved radial velocity in the ARL cross-beam direction improves to 90-94%. By using the dual-lidar retrieved data as a reference, the single-lidar 4DVAR is able to recover fluctuating velocity fields with 70-80% accuracy in the along-beam direction and 60-70% accuracy in the cross-beam direction. Large-scale convective roll structures are found in the vicinity of downtown airpark and parks. Vortical structures are identified near the business district. Strong updrafts and downdrafts are also found above a cluster of restaurants.« less

Studies of Copper, Silver, and Gold Cluster Anions: Evidence of Electronic Shell Structure.

NASA Astrophysics Data System (ADS)

Pettiette, Claire Lynn

A new Ultraviolet Magnetic Time-of-Flight Photoelectron Spectrometer (MTOFPES) has been developed for the study of the electronic structure of clusters produced in a pulsed supersonic molecular beam. This is the first technique which has been successful in probing the valence electronic states of metal clusters. The ultraviolet photoelectron spectra of negative cluster ions of the noble metals have been taken at several different photon energies. These are presented along with the electron affinity and HOMO-LUMO gap measurements for Cu_6^- to Cu_ {41}^-, using 4.66 eV and 6.42 eV detachment energies; Ag_3^- to Ag_{21}^-, using 6.42 eV detachment energy; and Au_3^ - to Au_{21}^-, using 6.42 eV and 7.89 eV detachment energies. The spectra provide the first detailed probes of the s valence electrons of the noble metal clusters. In addition, the 6.42 eV and 7.89 eV spectra probe the first one to two electron volts of the molecular orbitals of the d valence electrons of copper and gold clusters. The electron affinity and HOMO-LUMO gap measurements of the noble metal clusters agree with the predictions of the ellipsoidal shell model for mono-valent metal clusters. In particular, cluster numbers 8, 20, and 40--which correspond to the spherical shell closings of this model--have low electron affinities and large HOMO-LUMO gaps. The spectra of the gold cluster ions indicate that the molecular orbital energies of the cluster valence electrons are more widely spaced for gold than for copper or silver. This is to be expected for the heavy atom clusters when relativistic effects are taken into account.

THE POPULATION OF COMPACT RADIO SOURCES IN THE ORION NEBULA CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbrich, J.; Meingast, S.; Rivilla, V. M.

We present a deep centimeter-wavelength catalog of the Orion Nebula Cluster (ONC), based on a 30 hr single-pointing observation with the Karl G. Jansky Very Large Array in its high-resolution A-configuration using two 1 GHz bands centered at 4.7 and 7.3 GHz. A total of 556 compact sources were detected in a map with a nominal rms noise of 3 μ Jy bm{sup −1}, limited by complex source structure and the primary beam response. Compared to previous catalogs, our detections increase the sample of known compact radio sources in the ONC by more than a factor of seven. The newmore » data show complex emission on a wide range of spatial scales. Following a preliminary correction for the wideband primary-beam response, we determine radio spectral indices for 170 sources whose index uncertainties are less than ±0.5. We compare the radio to the X-ray and near-infrared point-source populations, noting similarities and differences.« less

Tribological coatings for complex mechanical elements produced by supersonic cluster beam deposition of metal dichalcogenide nanoparticles

NASA Astrophysics Data System (ADS)

Piazzoni, C.; Buttery, M.; Hampson, M. R.; Roberts, E. W.; Ducati, C.; Lenardi, C.; Cavaliere, F.; Piseri, P.; Milani, P.

2015-07-01

Fullerene-like MoS2 and WS2 nanoparticles can be used as building blocks for the fabrication of fluid and solid lubricants. Metal dichalcogenide films have a very low friction coefficient in vacuum, therefore they have mostly been used as solid lubricants in space and vacuum applications. Unfortunately, their use is significantly hampered by the fact that in the presence of humidity, oxygen and moisture, the low-friction properties of these materials rapidly degrade due to oxidation. The use of closed-cage MoS2 and WS2 nanoparticles may eliminate this problem, although the fabrication of lubricant thin films starting from dichalcogenide nanoparticles is, to date, a difficult task. Here we demonstrate the use of supersonic cluster beam deposition for the coating of complex mechanical elements (angular contact ball bearings) with nanostructured MoS2 and WS2 thin films. We report structural and tribological characterization of the coatings in view of the optimization of tribological performances for aerospace applications.

A liquid-He cryostat for structural and thermal disorder studies by X-ray absorption.

PubMed

Bouamrane, F; Ribbens, M; Fonda, E; Adjouri, C; Traverse, A

2003-07-01

A new device operating from 4.2 to 300 K is now installed on the hard X-ray station of the DCI ring in LURE in order to measure absorption coefficients. This liquid-He bath device has three optical windows. One allows the incident beam to impinge on the sample, one located at 180 degrees with respect to the sample allows transmitted beams to be detected, and another located at 90 degrees is used to detect emitted photons. Total electron yield detection mode is also possible thanks to a specific sample holder equipped with an electrode that collects the charges created by the emitted electrons in the He gas brought from the He bath around the sample. The performance of the cryostat is described by measurements of the absorption coefficients versus the temperature for Cu and Co foils. For comparison, the absorption coefficient is also measured for Cu clusters. As expected from dimension effects, the Debye temperature obtained for the clusters is lower than that of bulk Cu.

Dual beam organic depth profiling using large argon cluster ion beams

PubMed Central

Holzweber, M; Shard, AG; Jungnickel, H; Luch, A; Unger, WES

2014-01-01

Argon cluster sputtering of an organic multilayer reference material consisting of two organic components, 4,4′-bis[N-(1-naphthyl-1-)-N-phenyl- amino]-biphenyl (NPB) and aluminium tris-(8-hydroxyquinolate) (Alq3), materials commonly used in organic light-emitting diodes industry, was carried out using time-of-flight SIMS in dual beam mode. The sample used in this study consists of a ∽400-nm-thick NPB matrix with 3-nm marker layers of Alq3 at depth of ∽50, 100, 200 and 300 nm. Argon cluster sputtering provides a constant sputter yield throughout the depth profiles, and the sputter yield volumes and depth resolution are presented for Ar-cluster sizes of 630, 820, 1000, 1250 and 1660 atoms at a kinetic energy of 2.5 keV. The effect of cluster size in this material and over this range is shown to be negligible. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons Ltd. PMID:25892830

Reprint of: Negative carbon cluster ion beams: New evidence for the special nature of C60

NASA Astrophysics Data System (ADS)

Liu, Y.; O'brien, S. C.; Zhang, Q.; Heath, J. R.; Tittel, F. K.; Curl, R. F.; Kroto, H. W.; Smalley, R. E.

2013-12-01

Cold carbon cluster negative ions are formed by supersonic expansion of a plasma created at the nozzle of a supersonic cluster beam source by an excimer laser pulse. The observed distribution of mass peaks for the Cn- ions for n > 40 demonstrates that the evidence previously given for the special stability of neutral C60 and the existence of spheroidal carbon shells cannot be an artifact of the ionization conditions.

SU-F-BRD-10: Lung IMRT Planning Using Standardized Beam Bouquet Templates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, L; Wu, Q J.; Yin, F

2014-06-15

Purpose: We investigate the feasibility of choosing from a small set of standardized templates of beam bouquets (i.e., entire beam configuration settings) for lung IMRT planning to improve planning efficiency and quality consistency, and also to facilitate automated planning. Methods: A set of beam bouquet templates is determined by learning from the beam angle settings in 60 clinical lung IMRT plans. A k-medoids cluster analysis method is used to classify the beam angle configuration into clusters. The value of the average silhouette width is used to determine the ideal number of clusters. The beam arrangements in each medoid of themore » resulting clusters are taken as the standardized beam bouquet for the cluster, with the corresponding case taken as the reference case. The resulting set of beam bouquet templates was used to re-plan 20 cases randomly selected from the database and the dosimetric quality of the plans was evaluated against the corresponding clinical plans by a paired t-test. The template for each test case was manually selected by a planner based on the match between the test and reference cases. Results: The dosimetric parameters (mean±S.D. in percentage of prescription dose) of the plans using 6 beam bouquet templates and those of the clinical plans, respectively, and the p-values (in parenthesis) are: lung Dmean: 18.8±7.0, 19.2±7.0 (0.28), esophagus Dmean: 32.0±16.3, 34.4±17.9 (0.01), heart Dmean: 19.2±16.5, 19.4±16.6 (0.74), spinal cord D2%: 47.7±18.8, 52.0±20.3 (0.01), PTV dose homogeneity (D2%-D99%): 17.1±15.4, 20.7±12.2 (0.03).The esophagus Dmean, cord D02 and PTV dose homogeneity are statistically better in the plans using the standardized templates, but the improvements (<5%) may not be clinically significant. The other dosimetric parameters are not statistically different. Conclusion: It's feasible to use a small number of standardized beam bouquet templates (e.g. 6) to generate plans with quality comparable to that of clinical plans. Partially supported by NIH/NCI under grant #R21CA161389 and a master research grant by Varian Medical System.« less

Growth of single-layer boron nitride dome-shaped nanostructures catalysed by iron clusters.

PubMed

Torre, A La; Åhlgren, E H; Fay, M W; Ben Romdhane, F; Skowron, S T; Parmenter, C; Davies, A J; Jouhannaud, J; Pourroy, G; Khlobystov, A N; Brown, P D; Besley, E; Banhart, F

2016-08-11

We report on the growth and formation of single-layer boron nitride dome-shaped nanostructures mediated by small iron clusters located on flakes of hexagonal boron nitride. The nanostructures were synthesized in situ at high temperature inside a transmission electron microscope while the e-beam was blanked. The formation process, typically originating at defective step-edges on the boron nitride support, was investigated using a combination of transmission electron microscopy, electron energy loss spectroscopy and computational modelling. Computational modelling showed that the domes exhibit a nanotube-like structure with flat circular caps and that their stability was comparable to that of a single boron nitride layer.

Cluster Beam Deposition of High Temperature Materials

DTIC Science & Technology

1991-01-01

include Secur y Classifocation) CLUSTER BEAM DEPOSITION OF HIGH TEMPERATURE MATERIALS 12 . PERSONAL AUTHOR(S) William J. Herron and James F. Garvey 13a TYPE... industria - applications (su:erconducting thin films, diamond-liKe !arbn,. films, patterned or multi-layered thin films, etc...) INT RODIU C’I 1 Recently there...Tne path of the expanc~ nr gas pulse passes perpendicularly (left to right in tne figure) over the surface of the target rod. I I Laser Beam-I I I Lens

Cluster mass estimators from CMB temperature and polarization lensing

NASA Astrophysics Data System (ADS)

Hu, Wayne; DeDeo, Simon; Vale, Chris

2007-12-01

Upcoming Sunyaev Zel'dovich surveys are expected to return ~104 intermediate mass clusters at high redshift. Their average masses must be known to the same accuracy as desired for the dark energy properties. Internal to the surveys, the cosmic microwave background (CMB) potentially provides a source for lensing mass measurements whose distance is precisely known and behind all clusters. We develop statistical mass estimators from six quadratic combinations of CMB temperature and polarization fields that can simultaneously recover large-scale structure and cluster mass profiles. The performance of these estimators on idealized Navarro Frenk White (NFW) clusters suggests that surveys with a ~1' beam and 10\\,\\muK^{\\prime} noise in uncontaminated temperature maps can make a ~10σ detection, or equivalently a ~10% mass measurement for each 103 set of clusters. With internal or external acoustic scale E-polarization measurements, the ET cross-correlation estimator can provide a stringent test for contaminants on a first detection at ~1/3 the significance. For surveys that reach below 3\\,\\muK^{\\prime}, the EB cross-correlation estimator should provide the most precise measurements and potentially the strongest control over contaminants.

Kinetic energy distribution of multiply charged ions in Coulomb explosion of Xe clusters.

PubMed

Heidenreich, Andreas; Jortner, Joshua

2011-02-21

We report on the calculations of kinetic energy distribution (KED) functions of multiply charged, high-energy ions in Coulomb explosion (CE) of an assembly of elemental Xe(n) clusters (average size (n) = 200-2171) driven by ultra-intense, near-infrared, Gaussian laser fields (peak intensities 10(15) - 4 × 10(16) W cm(-2), pulse lengths 65-230 fs). In this cluster size and pulse parameter domain, outer ionization is incomplete∕vertical, incomplete∕nonvertical, or complete∕nonvertical, with CE occurring in the presence of nanoplasma electrons. The KEDs were obtained from double averaging of single-trajectory molecular dynamics simulation ion kinetic energies. The KEDs were doubly averaged over a log-normal cluster size distribution and over the laser intensity distribution of a spatial Gaussian beam, which constitutes either a two-dimensional (2D) or a three-dimensional (3D) profile, with the 3D profile (when the cluster beam radius is larger than the Rayleigh length) usually being experimentally realized. The general features of the doubly averaged KEDs manifest the smearing out of the structure corresponding to the distribution of ion charges, a marked increase of the KEDs at very low energies due to the contribution from the persistent nanoplasma, a distortion of the KEDs and of the average energies toward lower energy values, and the appearance of long low-intensity high-energy tails caused by the admixture of contributions from large clusters by size averaging. The doubly averaged simulation results account reasonably well (within 30%) for the experimental data for the cluster-size dependence of the CE energetics and for its dependence on the laser pulse parameters, as well as for the anisotropy in the angular distribution of the energies of the Xe(q+) ions. Possible applications of this computational study include a control of the ion kinetic energies by the choice of the laser intensity profile (2D∕3D) in the laser-cluster interaction volume.

RHEED and EELS study of Pd/Al bimetallic thin film growth on different α-Al 2O 3 substrates

NASA Astrophysics Data System (ADS)

Moroz, V.; Rajs, K.; Mašek, K.

2002-06-01

Pd/Al bimetallic thin films were grown by molecular beam epitaxy on single-crystalline α-Al 2O 3(0 0 0 1) and (1 1 2¯ 0) surfaces. Substrate and deposit crystallographic structures and evolution of deposit lattice parameter during the growth were studied by reflection high-energy electron diffraction. The electron energy loss spectroscopy was used as an auxiliary method for chemical analysis. The bimetallic films were prepared by successive deposition of both Pd and Al metals. The structure of Pd and Al deposits in early stages of the growth and its dependence on the preparation conditions were studied. Two phases of Pd clusters covered by Al overlayer have been found. The formation of Al overlayer strongly influenced the lattice parameter of Pd clusters.

Study of MoVO(y) (y = 2-5) anion and neutral clusters using anion photoelectron spectroscopy and density functional theory calculations.

PubMed

Mann, Jennifer E; Rothgeb, David W; Waller, Sarah E; Jarrold, Caroline Chick

2010-10-28

The vibrationally resolved anion photoelectron (PE) spectra of MoVO(y)(-) (y = 2 - 5) metal suboxide clusters are presented and analyzed in the context of density functional theory (DFT) calculations. The electronically congested spectra reflect an increase in cluster electron affinity with increasing oxidation state. Ion beam hole-burning results reveal the features in the PE spectra of MoVO(2)(-) and MoVO(4)(-) are a result of only one anion isomer, while at least two isomers contribute to electronic structure observed in the PE spectrum of MoVO(3)(-). Spectral features of the binary systems are compared to their pure analogs, Mo(2)O(y) and V(2)O(y). An attempt to characterize the anion and neutral electronic and molecular structures is made by comparison with results from DFT calculations. However, reconciliation between the cluster spectra and the calculated spectroscopic parameters is not as straightforward as in previous studies on similar systems (Yoder, B. L.; Maze, J. T.; Raghavachari, K.; Jarrold, C. C. J. Chem. Phys. 2005, 122, 094313 and Mayhall, N. J.; Rothgeb, D. W.; Hossain, E.; Raghavachari, K.; Jarrold, C. C. J. Chem. Phys. 2009, 130, 124313).

Electronic spectra and excited-state dynamics of acridine and its hydrated clusters

NASA Astrophysics Data System (ADS)

Harthcock, Colin; Zhang, Jie; Kong, Wei; Mitsui, Masaaki; Ohshima, Yasuhiro

2017-04-01

We combine results from several different experiments to investigate the photophysics of acridine (Ac) and its hydrated clusters in the gas phase. Our findings are also compared with results from condensed phase studies. Similar to measurements of Ac dissolved in hydrocarbons, the lifetime of the first electronically excited state of isolated Ac in vacuum is too short for typical resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF) experiments, hence no signal from REMPI and LIF can be attributed to monomeric Ac. Instead, sensitized phosphorescence emission spectroscopy is more successful in revealing the electronic states of Ac. Upon clustering with water, on the other hand, the lifetimes of the excited states are substantially increased to the nanosecond scale, and with two water molecules attached to Ac, the lifetime of the hydrated cluster is essentially the same as that of Ac in aqueous solutions. Detailed REMPI and ultraviolet-ultraviolet hole-burning experiments are then performed to reveal the structural information of the hydrated clusters. Although the formation of hydrogen bonds results in energy level reversal and energy separation between the first two excited states of Ac, its effect on the internal geometry of Ac is minimal, and all clusters with 1-3 water molecules demonstrate consistent intramolecular vibrational modes. Theoretical calculations reveal just one stable structure for each cluster under supersonic molecular beam conditions. Furthermore, different from mono- and di-water clusters, tri-water clusters consist of a linear chain of three water molecules attached to Ac. Consequently, the fragmentation pattern in the REMPI spectrum of tri-water clusters seems to be dominated by water trimer elimination, since the REMPI spectrum of Ac+.W3 is largely reproduced in the Ac+ mass channel, but not in the Ac+.W1 or Ac+.W2 channel.

Measuring galaxy cluster masses with CMB lensing using a Maximum Likelihood estimator: statistical and systematic error budgets for future experiments

NASA Astrophysics Data System (ADS)

Raghunathan, Srinivasan; Patil, Sanjaykumar; Baxter, Eric J.; Bianchini, Federico; Bleem, Lindsey E.; Crawford, Thomas M.; Holder, Gilbert P.; Manzotti, Alessandro; Reichardt, Christian L.

2017-08-01

We develop a Maximum Likelihood estimator (MLE) to measure the masses of galaxy clusters through the impact of gravitational lensing on the temperature and polarization anisotropies of the cosmic microwave background (CMB). We show that, at low noise levels in temperature, this optimal estimator outperforms the standard quadratic estimator by a factor of two. For polarization, we show that the Stokes Q/U maps can be used instead of the traditional E- and B-mode maps without losing information. We test and quantify the bias in the recovered lensing mass for a comprehensive list of potential systematic errors. Using realistic simulations, we examine the cluster mass uncertainties from CMB-cluster lensing as a function of an experiment's beam size and noise level. We predict the cluster mass uncertainties will be 3 - 6% for SPT-3G, AdvACT, and Simons Array experiments with 10,000 clusters and less than 1% for the CMB-S4 experiment with a sample containing 100,000 clusters. The mass constraints from CMB polarization are very sensitive to the experimental beam size and map noise level: for a factor of three reduction in either the beam size or noise level, the lensing signal-to-noise improves by roughly a factor of two.

Electrochemical impedance spectroscopy on nanostructured carbon electrodes grown by supersonic cluster beam deposition

NASA Astrophysics Data System (ADS)

Bettini, Luca Giacomo; Bardizza, Giorgio; Podestà, Alessandro; Milani, Paolo; Piseri, Paolo

2013-02-01

Nanostructured porous films of carbon with density of about 0.5 g/cm3 and 200 nm thickness were deposited at room temperature by supersonic cluster beam deposition (SCBD) from carbon clusters formed in the gas phase. Carbon film surface topography, determined by atomic force microscopy, reveals a surface roughness of 16 nm and a granular morphology arising from the low kinetic energy ballistic deposition regime. The material is characterized by a highly disordered carbon structure with predominant sp2 hybridization as evidenced by Raman spectroscopy. The interface properties of nanostructured carbon electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy employing KOH 1 M solution as aqueous electrolyte. An increase of the double layer capacitance is observed when the electrodes are heat treated in air or when a nanostructured nickel layer deposited by SCBD on top of a sputter deposited film of the same metal is employed as a current collector instead of a plain metallic film. This enhancement is consistent with an improved charge injection in the active material and is ascribed to the modification of the electrical contact at the interface between the carbon and the metal current collector. Specific capacitance values up to 120 F/g have been measured for the electrodes with nanostructured metal/carbon interface.

Low-energy collisions of helium clusters with size-selected cobalt cluster ions

NASA Astrophysics Data System (ADS)

Odaka, Hideho; Ichihashi, Masahiko

2017-04-01

Collisions of helium clusters with size-selected cobalt cluster ions, Com+ (m ≤ 5), were studied experimentally by using a merging beam technique. The product ions, Com+Hen (cluster complexes), were mass-analyzed, and this result indicates that more than 20 helium atoms can be attached onto Com+ at the relative velocities of 103 m/s. The measured size distributions of the cluster complexes indicate that there are relatively stable complexes: Co2+Hen (n = 2, 4, 6, and 12), Co3+Hen (n = 3, 6), Co4+He4, and Co5+Hen (n = 3, 6, 8, and 10). These stabilities are explained in terms of their geometric structures. The yields of the cluster complexes were also measured as a function of the relative velocity (1 × 102-4 × 103 m/s), and this result demonstrates that the main interaction in the collision process changes with the increase of the collision energy from the electrostatic interaction, which includes the induced deformation of HeN, to the hard-sphere interaction. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80015-0

The Atacama Cosmology Telescope (ACT): Beam Profiles and First SZ Cluster Maps

NASA Technical Reports Server (NTRS)

Hincks, A. D.; Acquaviva, V.; Ade, P. A.; Aguirre, P.; Amiri, M.; Appel, J. W.; Barrientos, L. F.; Battistelli, E. S.; Bond, J. R.; Brown, B.;

Application of pulsed multi-ion irradiations in radiation damage research: A stochastic cluster dynamics simulation study

NASA Astrophysics Data System (ADS)

Hoang, Tuan L.; Nazarov, Roman; Kang, Changwoo; Fan, Jiangyuan

2018-07-01

Under the multi-ion irradiation conditions present in accelerated material-testing facilities or fission/fusion nuclear reactors, the combined effects of atomic displacements with radiation products may induce complex synergies in the structural materials. However, limited access to multi-ion irradiation facilities and the lack of computational models capable of simulating the evolution of complex defects and their synergies make it difficult to understand the actual physical processes taking place in the materials under these extreme conditions. In this paper, we propose the application of pulsed single/dual-beam irradiation as replacements for the expensive steady triple-beam irradiation to study radiation damages in materials under multi-ion irradiation.

21ST International Symposium on Rarefied Gas Dynamics. Marseille (France) 26-31 July 1998. Book of Abstracts: Volume III, Special Session; Molecular Beams.

DTIC Science & Technology

1998-07-30

contribution we will present size dependent results absorption.of photons from two ultrashort laser pulses on the dynamics of electronic excitations in the at a... cluster beam has confirmed that the nanoparticles in the gas phase and deposited in thin laser -driven flow reactor is capable of producing films. hydrogen ...approximately 7 times larger than neutrals. MB 11 - 138 Molecular Beam Studies of Ammonia Clustered with III Group Metals Produced by Pulsed Laser Reactive

Low Beam Voltage, 10 MW, L-Band Cluster Klystron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teryaev, V.; /Novosibirsk, IYF; Yakovlev, V.P.

2009-05-01

Conceptual design of a multi-beam klystron (MBK) for possible ILC and Project X applications is presented. The chief distinction between this MBK design and existing 10-MW MBK's is the low operating voltage of 60 kV. There are at least four compelling reasons that justify development at this time of a low-voltage MBK, namely (1) no pulse transformer; (2) no oil tank for high-voltage components and for the tube socket; (3) no high-voltage cables; and (4) modulator would be a compact 60-kV IGBT switching circuit. The proposed klystron consists of four clusters containing six beams each. The tube has common inputmore » and output cavities for all 24 beams, and individual gain cavities for each cluster. A closely related optional configuration, also for a 10 MW tube, would involve four totally independent cavity clusters with four independent input cavities and four 2.5 MW output ports, all within a common magnetic circuit. This option has appeal because the output waveguides would not require a controlled atmosphere, and because it would be easier to achieve phase and amplitude stability as required in individual SC accelerator cavities.« less

Applied anatomic site study of palatal anchorage implants using cone beam computed tomography.

PubMed

Lai, Ren-fa; Zou, Hui; Kong, Wei-dong; Lin, Wei

2010-06-01

The purpose of this study was to conduct quantitative research on bone height and bone mineral density of palatal implant sites for implantation, and to provide reference sites for safe and stable palatal implants. Three-dimensional reformatting images were reconstructed by cone beam computed tomography (CBCT) in 34 patients, aged 18 to 35 years, using EZ Implant software. Bone height was measured at 20 sites of interest on the palate. Bone mineral density was measured at the 10 sites with the highest implantation rate, classified using K-mean cluster analysis based on bone height and bone mineral density. According to the cluster analysis, 10 sites were classified into three clusters. Significant differences in bone height and bone mineral density were detected between these three clusters (P<0.05). The greatest bone height was obtained in cluster 2, followed by cluster 1 and cluster 3. The highest bone mineral density was found in cluster 3, followed by cluster 1 and cluster 2. CBCT plays an important role in pre-surgical treatment planning. CBCT is helpful in identifying safe and stable implantation sites for palatal anchorage.

D-Cluster Converter Foil for Laser-Accelerated Deuteron Beams: Towards Deuteron-Beam-Driven Fast Ignition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miley, George H.

Fast Ignition (FI) uses Petawatt laser generated particle beam pulse to ignite a small volume called a pre-compressed Inertial Confinement Fusion (ICF) target, and is the favored method to achieve the high energy gain per target burn needed for an attractive ICF power plant. Ion beams such as protons, deuterons or heavier carbon ions are especially appealing for FI as they have relative straight trajectory, and easier to focus on the fuel capsule. But current experiments have encountered problems with the 'converter-foil' which is irradiated by the Petawatt laser to produce the ion beams. The problems include depletion of themore » available ions in the convertor foils, and poor energy efficiency (ion beam energy/ input laser energy). We proposed to develop a volumetrically-loaded ultra-high-density deuteron deuterium cluster material as the basis for converter-foil for deuteron beam generation. The deuterons will fuse with the ICF DT while they slow down, providing an extra 'bonus' energy gain in addition to heating the hot spot. Also, due to the volumetric loading, the foil will provide sufficient energetic deuteron beam flux for 'hot spot' ignition, while avoiding the depletion problem encountered by current proton-driven FI foils. After extensive comparative studies, in Phase I, high purity PdO/Pd/PdO foils were selected for the high packing fraction D-Cluster converter foils. An optimized loading process has been developed to increase the cluster packing fraction in this type of foil. As a result, the packing fraction has been increased from 0.1% to 10% - meeting the original Phase I goal and representing a significant progress towards the beam intensities needed for both FI and pulsed neutron applications. Fast Ignition provides a promising approach to achieve high energy gain target performance needed for commercial Inertial Confinement Fusion (ICF). This is now a realistic goal for near term in view of the anticipated ICF target burn at the National Ignition Facility (NIF) in CA within a year. This will usher in the technology development Phase of ICF after years of research aimed at achieving breakeven experiment. Methods to achieve the high energy gain needed for a competitive power plant will then be a key developmental issue, and our D-cluster target for Fast Ignition (FI) is expected to meet that need.« less

Preparation and electrical-property characterization of poly(vinyl chloride)-derived carbon nanosheet by ion beam irradiation-induced carbon clustering and carbonization

NASA Astrophysics Data System (ADS)

Jung, Chan-Hee; Sohn, Joon-Yong; Kim, Hyo-Sub; Hwang, In-Tae; Lee, Hong-Joon; Shin, Junhwa; Choi, Jae-Hak

2018-05-01

In this work, we demonstrated that carbon nanosheet (CNS) can easily be produced by a room-temperature, solid-state proton irradiation-induced clustering of poly(vinyl chloride) (PVC) films followed by carbonization. The results of the optical, chemical, and structural analyses revealed that oxidized and sp2-hybridized carbon clusters were effectively created in the PVC thin film by combined dehydrochlorination and inter-coupling reactions during proton irradiation. This was further converted to pseudo-hexagonally-structured nano-crystalline CNS with 2-D symmetry and metallic transporting character by high-temperature treatment. As a result, the CNS exhibited a very high electrical conductivity (587 S/cm) without a significant change in their thickness, a low surface roughness (0.36 nm), and a high work function (5.11 eV). These findings demonstrate that the radiation-based approach opens new avenues for the design and development of 2-D CNS as a graphene allotrope for the application of electronic devices, including field-effect transistors, electric heating devices, biosensors, supercapacitors, and fuel cells.

Characterization of high explosive particles using cluster secondary ion mass spectrometry.

PubMed

Gillen, Greg; Mahoney, Christine; Wight, Scott; Lareau, Richard

2006-01-01

The use of secondary ion mass spectrometry (SIMS) for the detection and spatially resolved analysis of individual high explosive particles is described. A C(8) (-) carbon cluster primary ion beam was used in a commercial SIMS instrument to analyze samples of high explosives dispersed as particles on silicon substrates. In comparison with monatomic primary ion bombardment, the carbon cluster primary ion beam was found to greatly enhance characteristic secondary ion signals from the explosive compounds while causing minimal beam-induced degradation. The resistance of these compounds to degradation under ion bombardment allows explosive particles to be analyzed under high primary ion dose bombardment (dynamic SIMS) conditions, facilitating the rapid acquisition of spatially resolved molecular information. The use of cluster SIMS combined with computer control of the sample stage position allows for the automated identification and counting of explosive particle distributions on silicon surfaces. This will be useful for characterizing the efficiency of transfer of particulates in trace explosive detection portal collectors and/or swipes utilized for ion mobility spectrometry applications.

Structure and Electronic Properties of Ionized PAH Clusters

NASA Astrophysics Data System (ADS)

Joblin, Christine; Kokkin, Damian L.; Sabbah, Hassan; Bonnamy, Anthony; Dontot, Leo; Rapacioli, Mathias; Simon, Aude; Spiegelman, Fernand; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Falvo, Cyril; Gamboa, Antonio; Brechignac, Philippe; Garcia, Gustavo A.; Nahon, Laurent

2014-06-01

Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This suggestion is a motivation for further characterization of the properties of these clusters in particular when they are ionized. We have used a molecular beam coupled to the photoelectron-photoion coincidence spectrometer DELICIOUS II/ III at the VUV beamline DESIRS of the synchrotron SOLEIL to characterize the electronic properties of cationic coronene (C24H12) and pyrene (C16H10) clusters up to the pentamer and heptamer, respectively. These experimental results are analysed in the light of electronic structure calculations. Simulations of the properties of ionized PAH clusters are faced with the difficulty of describing charge delocalization in these large systems. We will show that recent developments combining a Density Functional Tight Binding method with Configuration Interaction scheme is successful in simulating the ionization potential, which gives strong confidence into the predicted structures for these PAH clusters. We will also present current effort to study charge transfer states by performing complementary measurements with the PIRENEA ion trap set-up. Joint ANR project GASPARIM, ANR-10-BLAN-501 M. Rapacioli, C. Joblin and P. Boissel Astron. & Astrophys., 429 (2005), 193-204. G. Garcia, H. Soldi-Lose and L. Nahon Rev. Sci. Instrum., 80 (2009), 023102; G. Garcia, B. Cunha de Miranda, M. Tia, S. Daly, L. Nahon, Rev. Sci. Instrum., 84 (2013), 053112 M. Rapacioli, A. Simon, L. Dontot and F. Spiegelman Phys. Status Solidi B, 249 (2) (2012), 245-258; L. Dontot, M. Rapacioli and F. Spiegelman (2014) submitted

Deuteron Beam Driven Fast Ignition of a Pre-Compressed Inertial Confinement Fusion (ICF) Fuel Capsule

NASA Astrophysics Data System (ADS)

Yang, Xiaoling; Miley, George; Flippo, Kirk; Hora, Heinrich; Gaillard, Sandrine; Offermann, Dustin

2012-10-01

We proposed to utilize a new ``Deuterium Cluster'' type structure for the laser interaction foil to generate an energetic deuteron beam as the fast igniter to ignite inertial confinement fusion fuel capsule. The benefit of deuteron beam driven fast ignition is that its deposition in the target fuel will not only provide heating but also fuse with fuel as they slow down in the target. The preliminary results from recent laser-deuteron acceleration experiment at LANL were encouraging. Also, in most recent calculations, we found that a 12.73% extra energy gain from deuteron beam-target fusion could be achieved when quasi-Maxwellian deuteron beam was assumed, and when a ρrb = 4.5 g/cm2 was considered, where ρ is the fuel density, and rb is the ion beam focusing radius on the target. These results provide some insight into the contribution of the extra heat produced by deuteron beam-target fusion to the hot spot ignition process. If the physics works as anticipated, this novel type of interaction foil can efficiently generate energetic deuterons during intense laser pulses. The massive yield of deuterons should turn out to be the most efficient way of igniting the DT fuel, making the dream of near-term commercialization of FI fusion more achievable.

Measuring galaxy cluster masses with CMB lensing using a Maximum Likelihood estimator: statistical and systematic error budgets for future experiments

DOE PAGES

Raghunathan, Srinivasan; Patil, Sanjaykumar; Baxter, Eric J.; ...

2017-08-25

We develop a Maximum Likelihood estimator (MLE) to measure the masses of galaxy clusters through the impact of gravitational lensing on the temperature and polarization anisotropies of the cosmic microwave background (CMB). We show that, at low noise levels in temperature, this optimal estimator outperforms the standard quadratic estimator by a factor of two. For polarization, we show that the Stokes Q/U maps can be used instead of the traditional E- and B-mode maps without losing information. We test and quantify the bias in the recovered lensing mass for a comprehensive list of potential systematic errors. Using realistic simulations, wemore » examine the cluster mass uncertainties from CMB-cluster lensing as a function of an experiment’s beam size and noise level. We predict the cluster mass uncertainties will be 3 - 6% for SPT-3G, AdvACT, and Simons Array experiments with 10,000 clusters and less than 1% for the CMB-S4 experiment with a sample containing 100,000 clusters. The mass constraints from CMB polarization are very sensitive to the experimental beam size and map noise level: for a factor of three reduction in either the beam size or noise level, the lensing signal-to-noise improves by roughly a factor of two.« less

Measuring galaxy cluster masses with CMB lensing using a Maximum Likelihood estimator: statistical and systematic error budgets for future experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghunathan, Srinivasan; Patil, Sanjaykumar; Baxter, Eric J.

We develop a Maximum Likelihood estimator (MLE) to measure the masses of galaxy clusters through the impact of gravitational lensing on the temperature and polarization anisotropies of the cosmic microwave background (CMB). We show that, at low noise levels in temperature, this optimal estimator outperforms the standard quadratic estimator by a factor of two. For polarization, we show that the Stokes Q/U maps can be used instead of the traditional E- and B-mode maps without losing information. We test and quantify the bias in the recovered lensing mass for a comprehensive list of potential systematic errors. Using realistic simulations, wemore » examine the cluster mass uncertainties from CMB-cluster lensing as a function of an experiment’s beam size and noise level. We predict the cluster mass uncertainties will be 3 - 6% for SPT-3G, AdvACT, and Simons Array experiments with 10,000 clusters and less than 1% for the CMB-S4 experiment with a sample containing 100,000 clusters. The mass constraints from CMB polarization are very sensitive to the experimental beam size and map noise level: for a factor of three reduction in either the beam size or noise level, the lensing signal-to-noise improves by roughly a factor of two.« less

Measuring galaxy cluster masses with CMB lensing using a Maximum Likelihood estimator: statistical and systematic error budgets for future experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghunathan, Srinivasan; Patil, Sanjaykumar; Bianchini, Federico

We develop a Maximum Likelihood estimator (MLE) to measure the masses of galaxy clusters through the impact of gravitational lensing on the temperature and polarization anisotropies of the cosmic microwave background (CMB). We show that, at low noise levels in temperature, this optimal estimator outperforms the standard quadratic estimator by a factor of two. For polarization, we show that the Stokes Q/U maps can be used instead of the traditional E- and B-mode maps without losing information. We test and quantify the bias in the recovered lensing mass for a comprehensive list of potential systematic errors. Using realistic simulations, wemore » examine the cluster mass uncertainties from CMB-cluster lensing as a function of an experiment's beam size and noise level. We predict the cluster mass uncertainties will be 3 - 6% for SPT-3G, AdvACT, and Simons Array experiments with 10,000 clusters and less than 1% for the CMB-S4 experiment with a sample containing 100,000 clusters. The mass constraints from CMB polarization are very sensitive to the experimental beam size and map noise level: for a factor of three reduction in either the beam size or noise level, the lensing signal-to-noise improves by roughly a factor of two.« less

Stopping and Coulomb explosion of energetic carbon clusters in a plasma irradiated by an intense laser field

NASA Astrophysics Data System (ADS)

Wang, Guiqiu; Wang, Younian

2015-09-01

The interaction of a charged particle beam with a plasma is a very important subject of relevance for many fields of physics, such as inertial confinement fusion (ICF) driven by ion or electron beams, high energy density physics, and related astrophysical problems. Recently, a promising ICF scheme has been proposed, in which the plasma target is irradiated simultaneously by intense laser and ion beams. For molecular ion or cluster, slowing down process will company the Coulomb explosion phenomenon. In this paper, we present a study of the effects of intense radiation field (RF) on the interaction of energetic carbon clusters in a plasma. The emphasis is laid on the dynamic polarization and correlation effects of the constituent ions within the cluster in order to disclose the role of the vicinage effects on the Coulomb explosion and energy deposition of the clusters in plasma. On the other hand, affecting of a strong laser field on the cluster propagating in plasma is considered, the influence of a large range of laser parameters and plasma parameters on the Coulomb explosion and stopping power are discussed. This work is supported by the National Natural Science Foundation of China (11375034), and the Fundamental Research Funds for the Central Universities of China (3132015144, 3132014337).

Uniform deposition of size-selected clusters using Lissajous scanning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beniya, Atsushi; Watanabe, Yoshihide, E-mail: e0827@mosk.tytlabs.co.jp; Hirata, Hirohito

2016-05-15

Size-selected clusters can be deposited on the surface using size-selected cluster ion beams. However, because of the cross-sectional intensity distribution of the ion beam, it is difficult to define the coverage of the deposited clusters. The aggregation probability of the cluster depends on coverage, whereas cluster size on the surface depends on the position, despite the size-selected clusters are deposited. It is crucial, therefore, to deposit clusters uniformly on the surface. In this study, size-selected clusters were deposited uniformly on surfaces by scanning the cluster ions in the form of Lissajous pattern. Two sets of deflector electrodes set in orthogonalmore » directions were placed in front of the sample surface. Triangular waves were applied to the electrodes with an irrational frequency ratio to ensure that the ion trajectory filled the sample surface. The advantages of this method are simplicity and low cost of setup compared with raster scanning method. The authors further investigated CO adsorption on size-selected Pt{sub n} (n = 7, 15, 20) clusters uniformly deposited on the Al{sub 2}O{sub 3}/NiAl(110) surface and demonstrated the importance of uniform deposition.« less

Live Dynamics of 53BP1 Foci Following Simultaneous Induction of Clustered and Dispersed DNA Damage in U2OS Cells

PubMed Central

Sollazzo, Alice; Brzozowska, Beata; Cheng, Lei; Lundholm, Lovisa; Scherthan, Harry

2018-01-01

Cells react differently to clustered and dispersed DNA double strand breaks (DSB). Little is known about the initial reaction to simultaneous induction of DSBs with different complexities. Here, we used live cell microscopy to analyse the behaviour of 53BP1-GFP (green fluorescence protein) foci formation at DSBs induced in U2OS cells by alpha particles, X-rays or mixed beams over a 75 min period post irradiation. X-ray-induced foci rapidly increased and declined over the observation interval. After an initial increase, mixed beam-induced foci remained at a constant level over the observation interval, similarly as alpha-induced foci. The average areas of radiation-induced foci were similar for mixed beams and X-rays, being significantly smaller than those induced by alpha particles. Pixel intensities were highest for mixed beam-induced foci and showed the lowest level of variability over time as compared to foci induced by alphas and X-rays alone. Finally, mixed beam-exposed foci showed the lowest level of mobility as compared to alpha and X-ray exposure. The results suggest paralysation of chromatin around foci containing clustered DNA damage. PMID:29419809

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

PubMed

Neustetter, M; Jabbour Al Maalouf, E; Limão-Vieira, P; Denifl, S

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n (+) (0 ≤ n ≤ 6) and W2(CO)n (+) (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n (+) (0 ≤ n ≤ 3) and W2C(CO)n (+) (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.

Application of Plasma Waveguides to High Energy Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milchberg, Howard M

2013-03-30

The eventual success of laser-plasma based acceleration schemes for high-energy particle physics will require the focusing and stable guiding of short intense laser pulses in reproducible plasma channels. For this goal to be realized, many scientific issues need to be addressed. These issues include an understanding of the basic physics of, and an exploration of various schemes for, plasma channel formation. In addition, the coupling of intense laser pulses to these channels and the stable propagation of pulses in the channels require study. Finally, new theoretical and computational tools need to be developed to aid in the design and analysismore » of experiments and future accelerators. Here we propose a 3-year renewal of our combined theoretical and experimental program on the applications of plasma waveguides to high-energy accelerators. During the past grant period we have made a number of significant advances in the science of laser-plasma based acceleration. We pioneered the development of clustered gases as a new highly efficient medium for plasma channel formation. Our contributions here include theoretical and experimental studies of the physics of cluster ionization, heating, explosion, and channel formation. We have demonstrated for the first time the generation of and guiding in a corrugated plasma waveguide. The fine structure demonstrated in these guides is only possible with cluster jet heating by lasers. The corrugated guide is a slow wave structure operable at arbitrarily high laser intensities, allowing direct laser acceleration, a process we have explored in detail with simulations. The development of these guides opens the possibility of direct laser acceleration, a true miniature analogue of the SLAC RF-based accelerator. Our theoretical studies during this period have also contributed to the further development of the simulation codes, Wake and QuickPIC, which can be used for both laser driven and beam driven plasma based acceleration schemes. We will continue our development of advanced simulation tools by modifying the QuickPIC algorithm to allow for the simulation of plasma particle pick-up by the wake fields. We have also performed extensive simulations of plasma slow wave structures for efficient THz generation by guided laser beams or accelerated electron beams. We will pursue experimental studies of direct laser acceleration, and THz generation by two methods, ponderomotive-induced THz polarization, and THz radiation by laser accelerated electron beams. We also plan to study both conventional and corrugated plasma channels using our new 30 TW in our new lab facilities. We will investigate production of very long hydrogen plasma waveguides (5 cm). We will study guiding at increasing power levels through the onset of laser-induced cavitation (bubble regime) to assess the role played by the preformed channel. Experiments in direct acceleration will be performed, using laser plasma wakefields as the electron injector. Finally, we will use 2-colour ionization of gases as a high frequency THz source (<60 THz) in order for femtosecond measurements of low plasma densities in waveguides and beams.« less

Building mechanical Greenberger-Horne-Zeilinger and cluster states by harnessing optomechanical quantum steerable correlations

NASA Astrophysics Data System (ADS)

Tan, Huatang; Wei, Yanghua; Li, Gaoxiang

2017-11-01

Greenberger-Horne-Zeilinger (GHZ) and cluster states are two typical kinds of multipartite entangled states and can respectively be used for realizing quantum networks and one-way computation. We propose a feasible scheme for generating Gaussian GHZ and cluster states of multiple mechanical oscillators by pulsed cavity optomechanics. In our scheme, each optomechanical cavity is driven by a blue-detuned pulse to establish quantum steerable correlations between the cavity output field and the mechanical oscillator, and the cavity outputs are combined at a beam-splitter array with given transmissivity and reflectivity for each beam splitter. We show that by harnessing the light-mechanical steerable correlations, the mechanical GHZ and cluster states can be realized via homodyne detection on the amplitude and phase quadratures of the output fields from the beam-splitter array. These achieved mechanical entangled states can be viewed as the output states of an effective mechanical beam-splitter array with the mechanical inputs prepared in squeezed states with the light-mechanical steering. The effects of detection efficiency and thermal noise on the achieved mechanical states are investigated. The present scheme does not require externally injected squeezing and it can also be applicable to other systems such as light-atomic-ensemble interface, apart from optomechanical systems.

Method of using deuterium-cluster foils for an intense pulsed neutron source

DOEpatents

Miley, George H.; Yang, Xiaoling

2013-09-03

A method is provided for producing neutrons, comprising: providing a converter foil comprising deuterium clusters; focusing a laser on the foil with power and energy sufficient to cause deuteron ions to separate from the foil; and striking a surface of a target with the deuteron ions from the converter foil with energy sufficient to cause neutron production by a reaction selected from the group consisting of D-D fusion, D-T fusion, D-metal nuclear spallation, and p-metal. A further method is provided for assembling a plurality of target assemblies for a target injector to be used in the previously mentioned manner. A further method is provided for producing neutrons, comprising: splitting a laser beam into a first beam and a second beam; striking a first surface of a target with the first beam, and an opposite second surface of the target with the second beam with energy sufficient to cause neutron production.

Electrostatic wire for stabilizing a charged particle beam

DOEpatents

Prono, Daniel S.; Caporaso, George J.; Briggs, Richard J.

1985-01-01

In combination with a charged particle beam generator and accelerator, apparatus and method are provided for stabilizing a beam of electrically charged particles. A guiding means, disposed within the particle beam, has an electric charge induced upon it by the charged particle beam. Because the sign of the electric charge on the guiding means and the sign of the particle beam are opposite, the particles are attracted toward and cluster around the guiding means to thereby stabilize the particle beam as it travels.

Electrostatic wire stabilizing a charged particle beam

DOEpatents

Prono, D.S.; Caporaso, G.J.; Briggs, R.J.

1983-03-21

In combination with a charged particle beam generator and accelerator, apparatus and method are provided for stabilizing a beam of electrically charged particles. A guiding means, disposed within the particle beam, has an electric charge induced upon it by the charged particle beam. Because the sign of the electric charge on the guiding means and the sign of the particle beam are opposite, the particles are attracted toward and cluster around the guiding means to thereby stabilize the particle beam as it travels.

Beam power-dependent laser-induced fluorescence radiation quenching of silver-ion-exchanged glasses

NASA Astrophysics Data System (ADS)

Nahal, Arashmid; Khalesifard, Hamid Reza M.

2007-04-01

In this article, results of an investigation about the modification of silver ions embedded in a glass matrix under the action of a CW high-power Ar + laser beam, by means of laser-induced fluorescence, is reported. It is known [A. Nahal, H.R.M. Khalesifard, J. Mostafavi-Amjad, Appl. Phys. B 79 (2004) 513-518] that, as a result of the interaction of the laser beam with the sample, the embedded silver ions reduce to neutral ones and silver clusters are formed. We observed that the fluorescence radiation of the central part of the interaction area, on the sample, diminishes simultaneously with the formation of the neutral clusters. Further increase in the exposure time or the power of the beam results in reappearance of the fluorescence radiation, in the central part of the interaction area. We found that, during and after the interaction the spectrum of the fluorescence radiation changes. This makes it possible to study the laser-induced changes in the embedded silver ions and clusters, in real-time.

The comptonization parameter from simulations of single-frequency, single-dish, dual-beam, cm-wave observations of galaxy clusters and mitigating CMB confusion using the Planck sky survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lew, Bartosz; Roukema, Boudewijn F., E-mail: blew@astro.uni.torun.pl, E-mail: boud@astro.uni.torun.pl

2016-11-01

Systematic effects in dual-beam, differential, radio observations of extended objects are discussed in the context of the One Centimeter Receiver Array (OCRA). We use simulated samples of Sunyaev-Zel'dovich (SZ) galaxy clusters at low ( z < 0.4) and intermediate (0.4 < z < 1.0) redshifts to study the implications of operating at a single frequency (30 GHz) on the accuracy of extracting SZ flux densities and of reconstructing comptonization parameters with OCRA. We analyze dependences on cluster mass, redshift, observation strategy, and telescope pointing accuracy. Using Planck data to make primary cosmic microwave background (CMB) templates, we test the feasibilitymore » of mitigating CMB confusion effects in observations of SZ profiles at angular scales larger than the separation of the receiver beams.« less

Nanoscale alloys and core-shell materials: Model predictions of the nanostructure and mechanical properties

NASA Astrophysics Data System (ADS)

Zhurkin, E. E.; van Hoof, T.; Hou, M.

2007-06-01

Atomic scale modeling methods are used to investigate the relationship between the properties of clusters of nanometer size and the materials that can be synthesized by assembling them. The examples of very different bimetallic systems are used. The first one is the Ni3Al ordered alloy and the second is the AgCo core-shell system. While the Ni3Al cluster assembled materials modeling is already reported in our previous work, here we focus on the prediction of new materials synthesized by low energy deposition and accumulation of AgCo clusters. It is found that the core-shell structure is preserved by deposition with energies typical of low energy cluster beam deposition, although deposition may induce substantial cluster deformation. In contrast with Ni3Al deposited cluster assemblies, no grain boundary between clusters survives deposition and the silver shells merge into a noncrystalline system with a layered structure, in which the fcc Co grains are embedded. To our knowledge, such a material has not yet been synthesized experimentally. Mechanical properties are discussed by confronting the behaviors of Ni3Al and AgCo under the effect of a uniaxial load. To this end, a molecular dynamics scheme is established in view of circumventing rate effects inherent to short term modeling and thereby allowing to examine large plastic deformation mechanisms. Although the mechanisms are different, large plastic deformations are found to improve the elastic properties of both the Ni3Al and AgCo systems by stabilizing their nanostructure. Beyond this improvement, when the load is further increased, the Ni3Al system displays reduced ductility while the AgCo system is superplastic. The superplasticity is explained by the fact that the layered structure of the Ag system is not modified by the deformation. Some coalescence of the Co grains is identified as a geometrical effect and is suggested to be a limiting factor to superplasticity.

Characterization of deuterium clusters mixed with helium gas for an application in beam-target-fusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bang, W.; Quevedo, H. J.; Bernstein, A. C.

We measured the average deuterium cluster size within a mixture of deuterium clusters and helium gas by detecting Rayleigh scattering signals. The average cluster size from the gas mixture was comparable to that from a pure deuterium gas when the total backing pressure and temperature of the gas mixture were the same as those of the pure deuterium gas. According to these measurements, the average size of deuterium clusters depends on the total pressure and not the partial pressure of deuterium in the gas mixture. To characterize the cluster source size further, a Faraday cup was used to measure themore » average kinetic energy of the ions resulting from Coulomb explosion of deuterium clusters upon irradiation by an intense ultrashort pulse. The deuterium ions indeed acquired a similar amount of energy from the mixture target, corroborating our measurements of the average cluster size. As the addition of helium atoms did not reduce the resulting ion kinetic energies, the reported results confirm the utility of using a known cluster source for beam-target-fusion experiments by introducing a secondary target gas.« less

Hydrogen bonding interaction of small acetaldehyde clusters studied with core-electron excitation spectroscopy in the oxygen K-edge region

NASA Astrophysics Data System (ADS)

Tabayashi, K.; Chohda, M.; Yamanaka, T.; Tsutsumi, Y.; Takahashi, O.; Yoshida, H.; Taniguchi, M.

2010-06-01

In order to examine inner-shell electron excitation spectra of molecular clusters with strong multipole interactions, excitation spectra and time-of-flight (TOF) fragment-mass spectra of small acetaldehyde (AA) clusters have been studied under the beam conditions. The TOF spectra at the oxygen K-edge region showed an intense growth of the protonated clusters, MnH+ (M=CH3CHO) in the cluster beams. "cluster-specific" excitation spectra could be generated by monitoring partial-ion-yields of the protonated clusters. The most intense band of O1s→π*CO was found to shift to a higher energy by 0.15 eV relative to the monomer band upon clusterization. X-ray absorption spectra (XAS) were also calculated for the representative dimer configurations using a computer modelling program based on the density functional theory. The XAS prediction for the most stable (non-planar) configuration was found to give a close comparison with the cluster-band shift observed. The band shift was interpreted as being due to the HOMO-LUMO interaction within the complex where a contribution of vibrationally blue-shifting hydrogen bonding could be identified.

Characterization of deuterium clusters mixed with helium gas for an application in beam-target-fusion experiments

DOE PAGES

Bang, W.; Quevedo, H. J.; Bernstein, A. C.; ...

2014-12-10

We measured the average deuterium cluster size within a mixture of deuterium clusters and helium gas by detecting Rayleigh scattering signals. The average cluster size from the gas mixture was comparable to that from a pure deuterium gas when the total backing pressure and temperature of the gas mixture were the same as those of the pure deuterium gas. According to these measurements, the average size of deuterium clusters depends on the total pressure and not the partial pressure of deuterium in the gas mixture. To characterize the cluster source size further, a Faraday cup was used to measure themore » average kinetic energy of the ions resulting from Coulomb explosion of deuterium clusters upon irradiation by an intense ultrashort pulse. The deuterium ions indeed acquired a similar amount of energy from the mixture target, corroborating our measurements of the average cluster size. As the addition of helium atoms did not reduce the resulting ion kinetic energies, the reported results confirm the utility of using a known cluster source for beam-target-fusion experiments by introducing a secondary target gas.« less

Anisotropic Etching Using Reactive Cluster Beams

NASA Astrophysics Data System (ADS)

Koike, Kunihiko; Yoshino, Yu; Senoo, Takehiko; Seki, Toshio; Ninomiya, Satoshi; Aoki, Takaaki; Matsuo, Jiro

2010-12-01

The characteristics of Si etching using nonionic cluster beams with highly reactive chlorine-trifluoride (ClF3) gas were examined. An etching rate of 40 µm/min or higher was obtained even at room temperature when a ClF3 molecular cluster was formed and irradiated on a single-crystal Si substrate in high vacuum. The etching selectivity of Si with respect to a photoresist and SiO2 was at least 1:1000. We also succeeded in highly anisotropic etching with an aspect ratio of 10 or higher. Moreover, this etching method has a great advantage of low damage, compared with the conventional plasma process.

Gas cluster ion beam assisted NiPt germano-silicide formation on SiGe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozcan, Ahmet S., E-mail: asozcan@us.ibm.com; Lavoie, Christian; Jordan-Sweet, Jean

We report the formation of very uniform and smooth Ni(Pt)Si on epitaxially grown SiGe using Si gas cluster ion beam treatment after metal-rich silicide formation. The gas cluster ion implantation process was optimized to infuse Si into the metal-rich silicide layer and lowered the NiSi nucleation temperature significantly according to in situ X-ray diffraction measurements. This novel method which leads to more uniform films can also be used to control silicide depth in ultra-shallow junctions, especially for high Ge containing devices, where silicidation is problematic as it leads to much rougher interfaces.

Evidence that Clouds of keV Hydrogen Ion Clusters Bounce Elastically from a Solid Surface

NASA Technical Reports Server (NTRS)

Lewis, R. A.; Martin, James J.; Chakrabarti, Suman; Rodgers, Stephen L. (Technical Monitor)

2002-01-01

The behavior of hydrogen ion clusters is tested by an inject/hold/extract technique in a Penning-Malmberg trap. The timing pattern of the extraction signals is consistent with the clusters bouncing elastically from a detector several times. The ion clusters behave more like an elastic fluid than a beam of ions.

Femtosecond laser structuring of silver-containing glass: Silver redistribution, selective etching, and surface topology engineering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desmoulin, Jean-Charles; Petit, Yannick; Cardinal, Thierry, E-mail: thierry.cardinal@icmcb.cnrs.fr

2015-12-07

Femtosecond direct laser writing in silver-containing phosphate glasses allows for the three-dimensional (3D) implementation of complex photonic structures. Sample translation along or perpendicular to the direction of the beam propagation has been performed, which led to the permanent formation of fluorescent structures, either corresponding to a tubular shape or to two parallel planes at the vicinity of the interaction voxel, respectively. These optical features are related to significant modifications of the local material chemistry. Indeed, silver depletion areas with a diameter below 200 nm were evidenced at the center of the photo-produced structures while photo-produced luminescence properties are attributed to themore » formation of silver clusters around the multiphoton interaction voxel. The laser-triggered oxidation-reduction processes and the associated photo-induced silver redistribution are proposed to be at the origin of the observed original 3D luminescent structures. Thanks to such material structuring, surface engineering has been also demonstrated. Selective surface chemical etching of the glass has been obtained subsequently to laser writing at the location of the photo-produced structures, revealing features with nanometric depth profiles and radial dimensions strongly related to the spatial distributions of the silver clusters.« less

Simulations of cm-wavelength Sunyaev-Zel'dovich galaxy cluster and point source blind sky surveys and predictions for the RT32/OCRA-f and the Hevelius 100-m radio telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lew, Bartosz; Kus, Andrzej; Birkinshaw, Mark

We investigate the effectiveness of blind surveys for radio sources and galaxy cluster thermal Sunyaev-Zel'dovich effects (TSZEs) using the four-pair, beam-switched OCRA-f radiometer on the 32-m radio telescope in Poland. The predictions are based on mock maps that include the cosmic microwave background, TSZEs from hydrodynamical simulations of large scale structure formation, and unresolved radio sources. We validate the mock maps against observational data, and examine the limitations imposed by simplified physics. We estimate the effects of source clustering towards galaxy clusters from NVSS source counts around Planck-selected cluster candidates, and include appropriate correlations in our mock maps. The studymore » allows us to quantify the effects of halo line-of-sight alignments, source confusion, and telescope angular resolution on the detections of TSZEs. We perform a similar analysis for the planned 100-m Hevelius radio telescope (RTH) equipped with a 49-beam radio camera and operating at frequencies up to 22 GHz.We find that RT32/OCRA-f will be suitable for small-field blind radio source surveys, and will detect 33{sup +17}{sub −11} new radio sources brighter than 0.87 mJy at 30 GHz in a 1 deg{sup 2} field at > 5σ CL during a one-year, non-continuous, observing campaign, taking account of Polish weather conditions. It is unlikely that any galaxy cluster will be detected at 3σ CL in such a survey. A 60-deg{sup 2} survey, with field coverage of 2{sup 2} beams per pixel, at 15 GHz with the RTH, would find <1.5 galaxy clusters per year brighter than 60 μJy (at 3σ CL), and would detect about 3.4 × 10{sup 4} point sources brighter than 1 mJy at 5σ CL, with confusion causing flux density errors ∼< 2% (20%) in 68% (95%) of the detected sources.A primary goal of the planned RTH will be a wide-area (π sr) radio source survey at 15 GHz. This survey will detect nearly 3 × 10{sup 5} radio sources at 5σ CL down to 1.3 mJy, and tens of galaxy clusters, in one year of operation with typical weather conditions. Confusion will affect the measured flux densities by ∼< 1.5% (16%) for 68% (95%) of the point sources. We also gauge the impact of the RTH by investigating its performance if equipped with the existing RT32 receivers, and the performance of the RT32 equipped with the RTH radio camera.« less

Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions

NASA Astrophysics Data System (ADS)

Bell, R. C.; Zemski, K. A.; Justes, D. R.; Castleman, A. W.

2001-01-01

The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vaporization source. The dominant peaks in the anion total mass distribution correspond to clusters having stoichiometries of the form (VO2)n(VO3)m(O2)q-. Collision-induced dissociation studies of the vanadium oxide species V2O4-6-, V3O6-9-, V4O8-10-, V5O11-13-, V6O13-15-, and V7O16-18- indicate that VO2, VO3, and V2O5 units are the main building blocks of these clusters. There are many similarities between the anion mass distribution and that of the cation distribution studied previously. The principal difference is a shift to higher oxygen content by one additional oxygen atom for the stoichiometric anions (VxOy-) as compared to the cations with the same number of vanadium atoms, which is attributed to the extra pair of electrons of the anionic species. The oxygen-rich clusters, VxOy(O2)-, are shown to more tightly adsorb molecular oxygen than those of the corresponding cationic clusters. In addition, the bond dissociation thresholds for the vanadium oxide clusters ΔE(V+-O)=6.09±0.28 eV, ΔE(OV+-O)=3.51±0.36 eV, and ΔE(O2V--O)=5.43±0.31 eV are determined from the energy-dependent collision-induced dissociation cross sections with Xe as the collision partner. To the best of our knowledge, this is the first bond dissociation energy reported for the breaking of the V-O bond of a vanadium oxide anion.

On the statistics of proto-cluster candidates detected in the Planck all-sky survey

NASA Astrophysics Data System (ADS)

Negrello, M.; Gonzalez-Nuevo, J.; De Zotti, G.; Bonato, M.; Cai, Z.-Y.; Clements, D.; Danese, L.; Dole, H.; Greenslade, J.; Lapi, A.; Montier, L.

2017-09-01

Observational investigations of the abundance of massive precursors of local galaxy clusters ('proto-clusters') allow us to test the growth of density perturbations, to constrain cosmological parameters that control it, to test the theory of non-linear collapse and how the galaxy formation takes place in dense environments. The Planck collaboration has recently published a catalogue of ≳2000 cold extragalactic sub-millimeter sources, I.e. with colours indicative of z ≳ 2, almost all of which appear to be overdensities of star-forming galaxies. They are thus considered as proto-cluster candidates. Their number densities (or their flux densities) are far in excess of expectations from the standard scenario for the evolution of large-scale structure. Simulations based on a physically motivated galaxy evolution model show that essentially all cold peaks brighter than S545GHz = 500 mJy found in Planck maps after having removed the Galactic dust emission can be interpreted as positive Poisson fluctuations of the number of high-z dusty proto-clusters within the same Planck beam, rather then being individual clumps of physically bound galaxies. This conclusion does not change if an empirical fit to the luminosity function of dusty galaxies is used instead of the physical model. The simulations accurately reproduce the statistic of the Planck detections and yield distributions of sizes and ellipticities in qualitative agreement with observations. The redshift distribution of the brightest proto-clusters contributing to the cold peaks has a broad maximum at 1.5 ≤ z ≤ 3. Therefore follow-up of Planck proto-cluster candidates will provide key information on the high-z evolution of large scale structure.

Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neustetter, M.; Jabbour Al Maalouf, E.; Denifl, S., E-mail: Stephan.Denifl@uibk.ac.at, E-mail: plimaovieira@fct.unl.pt

2016-08-07

Electron ionization of neat tungsten hexacarbonyl (W(CO){sub 6}) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO){sub 6} clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO){sub n}{sup +} (0 ≤ n ≤ 6) and W{sub 2}(CO){sub n}{sup +} (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO){sub n}{sup +} (0 ≤more » n ≤ 3) and W{sub 2}C(CO){sub n}{sup +} (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.« less

Theory of liquid crystal orientation under action of light wave field and aligning surfaces

NASA Astrophysics Data System (ADS)

Dadivanyan, A. K.; Chausov, D. N.; Belyaev, V. V.; Barabanova, N. N.; Chausova, O. V.; Kuleshova, Yu D.

2018-03-01

Theoretical models developed in the MRSU group under leadership of Professor Artem Dadivanyan in area of the LC orientation and photo-induced effects are presented. Angular distribution functions of the dye and liquid crystal molecules under action of intensive light beam have been derived. The number of molecules in cluster is estimated. A model of dimers formation in the photoalignment dye is suggested that explains influence of the dye molecular structure on both polar and azimuthal anchoring energy.

Nucleation of Hydrogen Deficient Carbon Clusters in Circumstellar Envelopes of Carbon Stars

NASA Astrophysics Data System (ADS)

Chiong, C. C.; Asvany, O.; Balucani, N.; Lee, Y. T.; Kaiser, R. I.

2001-04-01

Hydrogen deficient carbon clusters HCn and H2Cn are thought to resemble the crucial link between naked carbon clusters such as C2/C3, polycyclic aromatic hydrocarbons, and carbon rich interstellar/circumstellar grains. To fully understand the astrophysical significance of these grain nuclei condensation processes, it is of paramount significance to elucidate first detailed mechanism how these simple precursors are formed in outflow of carbon rich stars. Due to this importance, we initiated in our laboratory a systematic research program to investigate reactions of C2 and C3 clusters in their singlet X1Σg+ ground state with unsaturated hydrocarbons C2H2 and C2H4 employing the crossed molecular beam technique. These experiments yield the first doubly differential reactive cross section on the cluster versus H/H2 exchange and supply valuable information on the stepwise growth of carbon rich structures in extraterrestrial environments. Preliminary data analyses identify the CCCCH, CCCCH, and CCCCH2 isomers which were identified in the circumstellar shell of IRC+10216 together with hitherto unobserved interstellar n-C4H3, n-C5H3, and CCCCCH2 radicals.

Physics with gamma-beams and charged particle detectors: I) Nuclear structure II) Nuclear astrophysics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gai, Moshe

The Charged Particle Working Group (CPWG) is proposing to construct large area Silicon Strip Detector (SSD), a gas Time Projection Chamber detector read by an electronic readout system (eTPC) and a Bubble Chamber (BC) containing superheated high purity water to be used in measurements utilizing intense gamma-ray beams from the newly constructed ELI-NP facility at Magurele, Bucharest in Romania. We intend to use the SSD and eTPC detectors to address essential problems in nuclear structure physics, such as clustering and the many alpha-decay of light nuclei such as {sup 12}C and {sup 16}O. All three detectors (SSD, eTPC and BC)more » will be used to address central problems in nuclear astrophysics such as the astrophysical cross section factor of the {sup 12}C(α,γ) reaction and other processes central to stellar evolution. The CPWG intends to submit to the ELI-NP facility a Technical Design Report (TDR) for the proposed detectors.« less

Structural, morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

NASA Astrophysics Data System (ADS)

Siddiqui, Jamil; Hussain, Tousif; Ahmad, Riaz; Umar, Zeeshan A.; Abdus Samad, Ubair

2016-05-01

The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10 cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10 cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4 ± 0.4 GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10 cm axial distance with 15 PFS.

Mixed clusters from the coexpansion of C2F6 and n2 in a pulsed, supersonic expansion cluster ion source and beam deflection time-of-flight mass spectrometer: A first application

NASA Astrophysics Data System (ADS)

Thompson, Steven D.

The following topics are discussed: (1) cluster ion genesis; (2) cluster ion detection; (3) Ion source; (4) pulse valve; (5) e-gun; (6) Ion optics; (7) a first order model; and (8) a modified Bakker's model.

Temperature-Dependent Evolution of the Oxidation States of Cobalt and Platinum in Co 1–xPt x Clusters under H 2 and CO + H 2 Atmospheres

DOE PAGES

Yang, Bing; Khadra, Ghassan; Tuaillon-Combes, Juliette; ...

2016-08-25

In this study, Co 1–xPt x clusters of 2.9-nm size with a range of atomically precise Pt/Co atomic ratios (x = 0, 0.25, 0.5, 0.75, 1) were synthesized using the mass-selected low-energy cluster beam deposition (LECBD) technique and soft-landed onto an amorphous alumina thin film prepared by atomic layer deposition (ALD). Utilizing ex situ X-ray photoemission spectroscopy (XPS), the oxidation state of the as-made clusters supported on Al 2O 3 was determined after both a 1-h-long exposure to air and aging for several weeks while exposed to air. Next, the aged cluster samples were characterized by grazing-incidence X-ray absorption spectroscopymore » (GIXAS) and then pretreated with diluted hydrogen and further exposed to the mixture of diluted CO and H 2 up to 225°C at atmospheric pressure, and the temperature-dependent evolutions of the particle size/shape and the oxidation states of the individual metal components within the clusters were monitored using in situ grazing-incidence small-angle X-ray scattering and X-ray absorption spectroscopy (GISAXS/GIXAS). The changes in the oxidation states of Co and Pt exhibited a nonlinear dependence on the Pt/Co atomic ratio of the clusters. For example, a low Pt/Co ratio (x ≤ 0.5) facilitates the formation of Co(OH) 2, whereas a high Pt/Co ratio (x = 0.75) stabilizes the Co 3O 4 composition instead through the formation of a Co–Pt core–shell structure where the platinum shell inhibits the reduction of cobalt in the core of the Co 1–xPt x alloy clusters. Finally, the obtained results indicate methods for optimizing the composition and structure of binary alloy clusters for catalysis.« less

Study of shallow junction formation by boron-containing cluster ion implantation of silicon and two-stage annealing

NASA Astrophysics Data System (ADS)

Lu, Xin-Ming

Shallow junction formation made by low energy ion implantation and rapid thermal annealing is facing a major challenge for ULSI (ultra large scale integration) as the line width decreases down to the sub micrometer region. The issues include low beam current, the channeling effect in low energy ion implantation and TED (transient enhanced diffusion) during annealing after ion implantation. In this work, boron containing small cluster ions, such as GeB, SiB and SiB2, was generated by using the SNICS (source of negative ion by cesium sputtering) ion source to implant into Si substrates to form shallow junctions. The use of boron containing cluster ions effectively reduces the boron energy while keeping the energy of the cluster ion beam at a high level. At the same time, it reduces the channeling effect due to amorphization by co-implanted heavy atoms like Ge and Si. Cluster ions have been used to produce 0.65--2keV boron for low energy ion implantation. Two stage annealing, which is a combination of low temperature (550°C) preannealing and high temperature annealing (1000°C), was carried out to anneal the Si sample implanted by GeB, SiBn clusters. The key concept of two-step annealing, that is, the separation of crystal regrowth, point defects removal with dopant activation from dopant diffusion, is discussed in detail. The advantages of the two stage annealing include better lattice structure, better dopant activation and retarded boron diffusion. The junction depth of the two stage annealed GeB sample was only half that of the one-step annealed sample, indicating that TED was suppressed by two stage annealing. Junction depths as small as 30 nm have been achieved by two stage annealing of sample implanted with 5 x 10-4/cm2 of 5 keV GeB at 1000°C for 1 second. The samples were evaluated by SIMS (secondary ion mass spectrometry) profiling, TEM (transmission electron microscopy) and RBS (Rutherford Backscattering Spectrometry)/channeling. Cluster ion implantation in combination with two-step annealing is effective in fabricating ultra-shallow junctions.

Continental Scale Vegetation Structure Mapping Using Field Calibrated Landsat, ALOS Palsar And GLAS ICESat

NASA Astrophysics Data System (ADS)

Scarth, P.; Phinn, S. R.; Armston, J.; Lucas, R.

2015-12-01

Vertical plant profiles are important descriptors of canopy structure and are used to inform models of biomass, biodiversity and fire risk. In Australia, an approach has been developed to produce large area maps of vertical plant profiles by extrapolating waveform lidar estimates of vertical plant profiles from ICESat/GLAS using large area segmentation of ALOS PALSAR and Landsat satellite image products. The main assumption of this approach is that the vegetation height profiles are consistent across the segments defined from ALOS PALSAR and Landsat image products. More than 1500 field sites were used to develop an index of fractional cover using Landsat data. A time series of the green fraction was used to calculate the persistent green fraction continuously across the landscape. This was fused with ALOS PALSAR L-band Fine Beam Dual polarisation 25m data and used to segment the Australian landscapes. K-means clustering then grouped the segments with similar cover and backscatter into approximately 1000 clusters. Where GLAS-ICESat footprints intersected these clusters, canopy profiles were extracted and aggregated to produce a mean vertical vegetation profile for each cluster that was used to derive mean canopy and understorey height, depth and density. Due to the large number of returns, these retrievals are near continuous across the landscape, enabling them to be used for inventory and modelling applications. To validate this product, a radiative transfer model was adapted to map directional gap probability from airborne waveform lidar datasets to retrieve vertical plant profiles Comparison over several test sites show excellent agreement and work is underway to extend the analysis to improve national biomass mapping. The integration of the three datasets provide options for future operational monitoring of structure and AGB across large areas for quantifying carbon dynamics, structural change and biodiversity.

Visual based laser speckle pattern recognition method for structural health monitoring

NASA Astrophysics Data System (ADS)

Park, Kyeongtaek; Torbol, Marco

2017-04-01

This study performed the system identification of a target structure by analyzing the laser speckle pattern taken by a camera. The laser speckle pattern is generated by the diffuse reflection of the laser beam on a rough surface of the target structure. The camera, equipped with a red filter, records the scattered speckle particles of the laser light in real time and the raw speckle image of the pixel data is fed to the graphic processing unit (GPU) in the system. The algorithm for laser speckle contrast analysis (LASCA) computes: the laser speckle contrast images and the laser speckle flow images. The k-mean clustering algorithm is used to classify the pixels in each frame and the clusters' centroids, which function as virtual sensors, track the displacement between different frames in time domain. The fast Fourier transform (FFT) and the frequency domain decomposition (FDD) compute the modal properties of the structure: natural frequencies and damping ratios. This study takes advantage of the large scale computational capability of GPU. The algorithm is written in Compute Unifies Device Architecture (CUDA C) that allows the processing of speckle images in real time.

Measurement of the spectral signature of small carbon clusters at near and far infrared wavelengths

NASA Technical Reports Server (NTRS)

Tarter, J.; Saykally, R.

1991-01-01

A significant percentage of the carbon inventory of the circumstellar and interstellar media may be in the form of large refractory molecules (or small grains) referred to as carbon clusters. At the small end, uneven numbers of carbon atoms seem to be preferred, whereas above 12 atoms, clusters containing an even number of carbon atoms appear to be preferred in laboratory chemistry. In the lab, the cluster C-60 appears to be a particularly stable form and has been nicknamed Bucky Balls because of its resemblance to a soccer ball and to geodesic domes designed by Buckminster Fuller. In order to investigate the prevalence of these clusters, and their relationship to the polycyclic aromatic hydrocarbons (PAHs) that have become the newest focus of IR astronomy, it is necessary to determine the spectroscopic characteristics of these clusters at near and far infrared wavelengths. Described here is the construction of a near to far IR laser magnetic resonance spectrometer that has been built at the University of California Berkeley in order to detect and characterize these spectra. The equipment produces carbon clusters by laser evaporation of a graphitic target. The clusters are then cooled in a supersonic expansion beam in order to simulate conditions in the interstellar medium (ISM). The expansion beam feeds into the spectrometer chamber and permits concentrations of clusters sufficiently high as to permit ultra-high resolution spectroscopy at near and far IR wavelengths. The first successful demonstration of this apparatus occurred last year when the laboratory studies permitted the observational detection of C-5 in the stellar outflow surrounding IRC+10216 in the near-IR. Current efforts focus on reducing the temperature of the supersonic expansion beam that transport the C clusters evaporated from a graphite target into the spectrometer down to temperatures as low as 1 K.

Unexpected materials in a Rembrandt painting characterized by high spatial resolution cluster-TOF-SIMS imaging.

PubMed

Sanyova, Jana; Cersoy, Sophie; Richardin, Pascale; Laprévote, Olivier; Walter, Philippe; Brunelle, Alain

2011-02-01

The painting materials of the Portrait of Nicolaes van Bambeeck (Royal Museums of Fine Arts of Belgium, Brussels, inv. 155) painted by Rembrandt van Rijn in 1641 has been studied using high resolution cluster-TOF-SIMS imaging. In the first step, a moderate spatial resolution (2 μm) was used to characterize the layer structure and the chemical composition of each layer on account of a high mass resolution. Then, in the second step, and despite a low mass resolution, the cluster primary ion beam was focused well below 1 μm in order to reveal smaller structures in the painting sample. The study confirmed the presence of starch in the second ground layer, which is quite surprising and, at least for Rembrandt paintings, has never been reported before. TOF-SIMS also indicated the presence of proteins, which, added to the size and shape of lake particles, suggests that it was manufactured from shearings (waste of textile manufacturing) of dyed wool, used as the source of the dyestuff. The analyses have also shown various lead carboxylates, being the products of the interaction between lead white and the oil of the binding medium. These findings considerably contribute to the understanding of Rembrandt's studio practice and thus demonstrate the importance and potential of cluster-TOF-SIMS imaging in the characterization on a submicrometer scale of artist painting materials.

Electronic Transport in Ultrathin Heterostructures.

DTIC Science & Technology

1981-10-01

heterostructures, superlattices, diffusion-enhanced disorder, transport properties, molecular beam epitaxy (MBE), photoluminescence, optical absorption...tion of single and multilayer GatlAs/GaAs heterostructures by metalorganic chemical vapor deposition (MJCVD) and molecular beam epitaxy (MBE) has...fundamental nature of these clusters and their relevance to other epitaxial techniques such as molecular beam epitaxy (MBE). To further varify or

Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skobelev, N. K., E-mail: skobelev@jinr.ru

2016-07-15

Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable ({sup 6}Li) and radioactive ({sup 6}He) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and {sup 3}He beams of the U-120M cyclotron at themore » Nuclear Physics Institute, Academy Sciences of Czech Republic (Řež and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei ({sup 6}Li and {sup 3}He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.« less

Dawn in the Apollo Valley

NASA Image and Video Library

2013-12-18

Beam Wave Guide antennas at Goldstone, known as the Beam Waveguide Cluster. They are located in an area at Goldstone called Apollo Valley. The Goldstone Deep Space Communications Complex is located in the Mojave Desert in California, USA.

Limited-angle multi-energy CT using joint clustering prior and sparsity regularization

NASA Astrophysics Data System (ADS)

Zhang, Huayu; Xing, Yuxiang

2016-03-01

In this article, we present an easy-to-implement Multi-energy CT scanning strategy and a corresponding reconstruction method, which facilitate spectral CT imaging by improving the data efficiency the number-of-energy- channel fold without introducing visible limited-angle artifacts caused by reducing projection views. Leveraging the structure coherence at different energies, we first pre-reconstruct a prior structure information image using projection data from all energy channels. Then, we perform a k-means clustering on the prior image to generate a sparse dictionary representation for the image, which severs as a structure information constraint. We com- bine this constraint with conventional compressed sensing method and proposed a new model which we referred as Joint Clustering Prior and Sparsity Regularization (CPSR). CPSR is a convex problem and we solve it by Alternating Direction Method of Multipliers (ADMM). We verify our CPSR reconstruction method with a numerical simulation experiment. A dental phantom with complicate structures of teeth and soft tissues is used. X-ray beams from three spectra of different peak energies (120kVp, 90kVp, 60kVp) irradiate the phantom to form tri-energy projections. Projection data covering only 75◦ from each energy spectrum are collected for reconstruction. Independent reconstruction for each energy will cause severe limited-angle artifacts even with the help of compressed sensing approaches. Our CPSR provides us with images free of the limited-angle artifact. All edge details are well preserved in our experimental study.

Mapper: high throughput maskless lithography

NASA Astrophysics Data System (ADS)

Kuiper, V.; Kampherbeek, B. J.; Wieland, M. J.; de Boer, G.; ten Berge, G. F.; Boers, J.; Jager, R.; van de Peut, T.; Peijster, J. J. M.; Slot, E.; Steenbrink, S. W. H. K.; Teepen, T. F.; van Veen, A. H. V.

2009-01-01

Maskless electron beam lithography, or electron beam direct write, has been around for a long time in the semiconductor industry and was pioneered from the mid-1960s onwards. This technique has been used for mask writing applications as well as device engineering and in some cases chip manufacturing. However because of its relatively low throughput compared to optical lithography, electron beam lithography has never been the mainstream lithography technology. To extend optical lithography double patterning, as a bridging technology, and EUV lithography are currently explored. Irrespective of the technical viability of both approaches, one thing seems clear. They will be expensive [1]. MAPPER Lithography is developing a maskless lithography technology based on massively-parallel electron-beam writing with high speed optical data transport for switching the electron beams. In this way optical columns can be made with a throughput of 10-20 wafers per hour. By clustering several of these columns together high throughputs can be realized in a small footprint. This enables a highly cost-competitive alternative to double patterning and EUV alternatives. In 2007 MAPPER obtained its Proof of Lithography milestone by exposing in its Demonstrator 45 nm half pitch structures with 110 electron beams in parallel, where all the beams where individually switched on and off [2]. In 2008 MAPPER has taken a next step in its development by building several tools. A new platform has been designed and built which contains a 300 mm wafer stage, a wafer handler and an electron beam column with 110 parallel electron beams. This manuscript describes the first patterning results with this 300 mm platform.

Electric dipole moments of nanosolvated acid molecules in water clusters.

PubMed

Guggemos, Nicholas; Slavíček, Petr; Kresin, Vitaly V

2015-01-30

The electric dipole moments of (H2O)nDCl (n=3-9) clusters have been measured by the beam-deflection method. Reflecting the (dynamical) charge distribution within the system, the dipole moment contributes information about the microscopic structure of nanoscale solvation. The addition of a DCl molecule to a water cluster results in a strongly enhanced susceptibility. There is evidence for a noticeable rise in the dipole moment occurring at n≈5-6. This size is consistent with predictions for the onset of ionic dissociation. Additionally, a molecular-dynamics model suggests that even with a nominally bound impurity an enhanced dipole moment can arise due to the thermal and zero-point motion of the proton and the water molecules. The experimental measurements and the calculations draw attention to the importance of fluctuations in defining the polarity of water-based nanoclusters and generally to the essential role played by motional effects in determining the response of fluxional nanoscale systems under realistic conditions.

Biocompatibility of cluster-assembled nanostructured TiO2 with primary and cancer cells.

PubMed

Carbone, Roberta; Marangi, Ida; Zanardi, Andrea; Giorgetti, Luca; Chierici, Elisabetta; Berlanda, Giuseppe; Podestà, Alessandro; Fiorentini, Francesca; Bongiorno, Gero; Piseri, Paolo; Pelicci, Pier Giuseppe; Milani, Paolo

2006-06-01

We have characterized the biocompatibility of nanostructured TiO2 films produced by the deposition of a supersonic beam of TiOx clusters. Physical analysis shows that these films possess, at the nanoscale, a granularity and porosity mimicking those of typical extracellular matrix structures and adsorption properties that could allow surface functionalization with different macromolecules such as DNA, proteins, and peptides. To explore the biocompatibility of this novel nanostructured surface, different cancer and primary cells were analyzed in terms of morphological appearance (by bright field microscopy and immunofluorescence) and growth properties, with the aim to evaluate cluster-assembled TiO2 films as substrates for cell-based and tissue-based applications. Our results strongly suggest that this new biomaterial supports normal growth and adhesion of primary and cancer cells with no need for coating with ECM proteins; we thus propose this new material as an optimal substrate for different applications in cell-based assays, biosensors or microfabricated medical devices.

Gold Nanoparticle Quantitation by Whole Cell Tomography.

PubMed

Sanders, Aric W; Jeerage, Kavita M; Schwartz, Cindi L; Curtin, Alexandra E; Chiaramonti, Ann N

2015-12-22

Many proposed biomedical applications for engineered gold nanoparticles require their incorporation by mammalian cells in specific numbers and locations. Here, the number of gold nanoparticles inside of individual mammalian stem cells was characterized using fast focused ion beam-scanning electron microscopy based tomography. Enhanced optical microscopy was used to provide a multiscale map of the in vitro sample, which allows cells of interest to be identified within their local environment. Cells were then serially sectioned using a gallium ion beam and imaged using a scanning electron beam. To confirm the accuracy of single cross sections, nanoparticles in similar cross sections were imaged using transmission electron microscopy and scanning helium ion microscopy. Complete tomographic series were then used to count the nanoparticles inside of each cell and measure their spatial distribution. We investigated the influence of slice thickness on counting single particles and clusters as well as nanoparticle packing within clusters. For 60 nm citrate stabilized particles, the nanoparticle cluster packing volume is 2.15 ± 0.20 times the volume of the bare gold nanoparticles.

Cluster Beam Deposition Technology for Optical Coatings. Phase 1

DTIC Science & Technology

1987-05-01

Particles 55 5.4.3 Growth of Ultrafine Particles or 61 Clusters by Gas Quenching 6.0 REFERENCES 67 APPENDIX: SUPPLEMENTARY INFORMATION 69 COP TR-407/5-87...approach, based on growth and transport of ultrafine particles or clusters in a quenching gas, appears more promising in our view and has been proposed for... Ultrafine Particles or Clusters by Gas quenching The apparent difficulty of making metal clusters with a Takagi-type source led us to explore other

Neutron Zeeman beam-splitting for the investigation of magnetic nanostructures

NASA Astrophysics Data System (ADS)

Kozhevnikov, S. V.; Ott, F.; Semenova, E.

2017-03-01

Zeeman spatial splitting of a neutron beam takes place during a neutron spin-flip in magnetically non-collinear systems at grazing incidence geometry. We apply the neutron beam-splitting method for the investigation of magnetically non-collinear clusters of submicron size in a thin film. The experimental results are compared with ones obtained by other methods.

Market segmentation and analysis of Japan's residential post and beam construction market.

Treesearch

Joseph A. Roos; Ivan L. Eastin; Hisaaki Matsuguma

2005-01-01

A mail survey of Japanese post and beam builders was conducted to measure their level of ethnocentrism, market orientation, risk aversion, and price consciousness. The data were analyzed utilizing factor and cluster analysis. The results showed that Japanese post and beam builders can be divided into three distinct market segments: open to import...

Linear self-focusing of continuous UV laser beam in photo-thermo-refractive glasses.

PubMed

Sidorov, Alexander I; Gorbyak, Veronika V; Nikonorov, Nikolay V

2018-03-19

The experimental and theoretical study of continuous UV laser beam propagation through thick silver-containing photo-thermo-refractive glass is presented. It is shown for the first time that self-action of UV Gaussian beam in glass results in its self-focusing. The observed linear effect is non-reversible and is caused by the transformation of subnanosized charged silver molecular clusters to neutral state under UV laser radiation. Such transformation is accompanied by the increase of molecular clusters polarizability and the refractive index increase in irradiated area. As a result, an extended positive lens is formed in glass bulk. In a theoretical study of linear self-focusing effect, the "aberration-free" approximation was used, taking into account spatial distribution of induced absorption.

Study of the photon remnant in resolved photoproduction at HERA

NASA Astrophysics Data System (ADS)

Derrick, M.; Krakauer, D.; Magill, S.; Mikunas, D.; Musgrave, B.; Repond, J.; Stanek, R.; Talaga, R. L.; Zhang, H.; Ayad, R.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Bruni, P.; Cara Romeo, G.; Castellini, G.; Chiarini, M.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; Gialas, I.; Giusti, P.; Iacobucci, G.; Laurenti, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Nemoz, C.; Palmonari, F.; Polini, A.; Sartorelli, G.; Timellini, R.; Zamora Garcia, Y.; Zichichi, A.; Bargende, A.; Crittenden, J.; Desch, K.; Diekmann, B.; Doeker, T.; Eckert, M.; Feld, L.; Frey, A.; Geerts, M.; Geitz, G.; Grothe, M.; Haas, T.; Hartmann, H.; Heinloth, K.; Hilger, E.; Jakob, H.-P.; Katz, U. F.; Mari, S. M.; Mass, A.; Mengel, S.; Mollen, J.; Paul, E.; Rembser, Ch; Schramm, D.; Stamm, J.; Wedemeyer, R.; Campbell-Robson, S.; Cassidy, A.; Dyce, N.; Foster, B.; George, S.; Gilmore, R.; Heath, G. P.; Heath, H. F.; Llewellyn, T. J.; Morgado, C. J. S.; Norman, D. J. P.; O'Mara, J. A.; Tapper, R. J.; Wilson, S. S.; Yoshida, R.; Rau, R. R.; Arneodo, M.; Iannotti, L.; Schioppa, M.; Susinno, G.; Bernstein, A.; Caldwell, A.; Cartiglia, N.; Parsons, J. A.; Ritz, S.; Sciulli, F.; Straub, P. B.; Wai, L.; Yang, S.; Zhu, Q.; Borzemski, P.; Chwastowski, J.; Eskreys, A.; Piotrzkowski, K.; Zachara, M.; Zawiejski, L.; Adamczyk, L.; Bednarek, B.; Jeleń, K.; Kisielewska, D.; Kowalski, T.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Zajaç, J.; Kotański, A.; Przybycień, M.; Bauerdick, L. A. T.; Behrens, U.; Beier, H.; Bienlein, J. K.; Coldewey, C.; Deppe, O.; Desler, K.; Drews, G.; Flasiński, M.; Gilkinson, D. J.; Glasman, C.; Göttlicher, P.; Große-Knetter, J.; Gutjahr, B.; Hain, W.; Hasell, D.; Heßling, H.; Iga, Y.; Joos, P.; Kasemann, M.; Klanner, R.; Koch, W.; Köpke, L.; Kötz, U.; Kowalski, H.; Labs, J.; Ladage, A.; Löhr, B.; Löwe, M.; Lüke, D.; Mainusch, J.; Mańczak, O.; Monteiro, T.; Ng, J. S. T.; Nickel, S.; Notz, D.; Ohrenberg, K.; Roco, M.; Rohde, M.; Roldán, J.; Schneekloth, U.; Schulz, W.; Selonke, F.; Stiliaris, E.; Surrow, B.; Voß, T.; Westphal, D.; Wolf, G.; Youngman, C.; Zhou, J. F.; Grabosch, H. J.; Kharchilava, A.; Leich, A.; Mattingly, M. C. K.; Meyer, A.; Schlenstedt, S.; Wulff, N.; Barbagli, G.; Pelfer, P.; Anzivino, G.; Maccarrone, G.; De Pasquale, S.; Votano, L.; Bamberger, A.; Eisenhardt, S.; Freidhof, A.; Söldner-Rembold, S.; Schroeder, J.; Trefzger, T.; Brook, N. H.; Bussey, P. J.; Doyle, A. T.; Fleck, J. I.; Saxon, D. H.; Utley, M. L.; Wilson, A. S.; Dannemann, A.; Holm, U.; Horstmann, D.; Neumann, T.; Sinkus, R.; Wick, K.; Badura, E.; Burow, B. D.; Hagge, L.; Lohrmann, E.; Milewski, J.; Nakahata, M.; Pavel, N.; Poelz, G.; Schott, W.; Zetsche, F.; Bacon, T. C.; Butterworth, I.; Gallo, E.; Harris, V. L.; Hung, B. Y. H.; Long, K. R.; Miller, D. B.; Morawitz, P. P. O.; Prinias, A.; Sedgbeer, J. K.; Whitfield, A. F.; Mallik, U.; McCliment, E.; Wang, M. Z.; Wang, S. M.; Wu, J. T.; Zhang, Y.; Cloth, P.; Filges, D.; An, S. H.; Hong, S. M.; Nam, S. W.; Park, S. K.; Suh, M. H.; Yon, S. H.; Imlay, R.; Kartik, S.; Kim, H.-J.; McNeil, R. R.; Metcalf, W.; Nadendla, V. K.; Barreiro, F.; Cases, G.; Fernandez, J. P.; Graciani, R.; Hernández, J. M.; Hervás, L.; Labarga, L.; Martinez, M.; del Peso, J.; Puga, J.; Terron, J.; de Trocóniz, J. F.; Smith, G. R.; Corriveau, F.; Hanna, D. S.; Hartmann, J.; Hung, L. W.; Lim, J. N.; Matthews, C. G.; Patel, P. M.; Sinclair, L. E.; Stairs, D. G.; St. Laurent, M.; Ullmann, R.; Zacek, G.; Bashkirov, V.; Dolgoshein, B. A.; Stifutkin, A.; Bashindzhagyan, G. L.; Ermolov, P. F.; Gladilin, L. K.; Golubkov, Y. A.; Kobrin, V. D.; Kuzmin, V. A.; Proskuryakov, A. S.; Savin, A. A.; Shcheglova, L. M.; Solomin, A. N.; Zotov, N. P.; Botje, M.; Chlebana, F.; Dake, A.; Engelen, J.; de Kamps, M.; Kooijman, P.; Kruse, A.; Tiecke, H.; Verkerke, W.; Vreeswijk, M.; Wiggers, L.; de Wolf, E.; van Woudenberg, R.; Acosta, D.; Bylsma, B.; Durkin, L. S.; Honscheid, K.; Li, C.; Ling, T. Y.; McLean, K. W.; Murray, W. N.; Park, I. H.; Romanowski, T. A.; Seidlein, R.; Bailey, D. S.; Byrne, A.; Cashmore, R. J.; Cooper-Sarkar, A. M.; Devenish, R. C. E.; Harnew, N.; Lancaster, M.; Lindemann, L.; McFall, J. D.; Nath, C.; Noyes, V. A.; Quadt, A.; Tickner, J. R.; Uijterwaal, H.; Walczak, R.; Waters, D. S.; Wilson, F. F.; Yip, T.; Abbiendi, G.; Bertolin, A.; Brugnera, R.; Carlin, R.; Dal Corso, F.; De Giorgi, M.; Dosselli, U.; Limentani, S.; Morandin, M.; Posocco, M.; Stanco, L.; Stroili, R.; Voci, C.; Bulmahn, J.; Butterworth, J. M.; Feild, R. G.; Oh, B. Y.; Whitmore, J. J.; D'Agostini, G.; Marini, G.; Nigro, A.; Tassi, E.; Hart, J. C.; McCubbin, N. A.; Prytz, K.; Shah, T. P.; Short, T. L.; Barberis, E.; Dubbs, T.; Heusch, C.; Van Hook, M.; Hubbard, B.; Lockman, W.; Rahn, J. T.; Sadrozinski, H. F.-W.; Seiden, A.; Biltzinger, J.; Seifert, R. J.; Schwarzer, O.; Walenta, A. H.; Zech, G.; Abramowicz, H.; Briskin, G.; Dagan, S.; Levy, A.; Hasegawa, T.; Hazumi, M.; Ishii, T.; Kuze, M.; Mine, S.; Nagasawa, Y.; Nakao, M.; Suzuki, I.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Chiba, M.; Hamatsu, R.; Hirose, T.; Homma, K.; Kitamura, S.; Nakamitsu, Y.; Yamauchi, K.; Cirio, R.; Costa, M.; Ferrero, M. I.; Lamberti, L.; Maselli, S.; Peroni, C.; Sacchi, R.; Solano, A.; Staiano, A.; Dardo, M.; Bailey, D. C.; Bandyopadhyay, D.; Benard, F.; Brkic, M.; Crombie, M. B.; Gingrich, D. M.; Hartner, G. F.; Joo, K. K.; Levman, G. M.; Martin, J. F.; Orr, R. S.; Sampson, C. R.; Teuscher, R. J.; Catterall, C. D.; Jones, T. W.; Kaziewicz, P. B.; Lane, J. B.; Saunders, R. L.; Shulman, J.; Blankenship, K.; Lu, B.; Mo, L. W.; Bogusz, W.; Charchuła, K.; Ciborowski, J.; Gajewski, J.; Grzelak, G.; Kasprzak, M.; Krzyżanowski, M.; Muchorowski, K.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Wróblewski, A. K.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Eisenberg, Y.; Karshon, U.; Revel, D.; Zer-Zion, D.; Ali, I.; Badgett, W. F.; Behrens, B.; Dasu, S.; Fordham, C.; Foudas, C.; Goussiou, A.; Loveless, R. J.; Reeder, D. D.; Silverstein, S.; Smith, W. H.; Vaiciulis, A.; Wodarczyk, M.; Tsurugai, T.; Bhadra, S.; Cardy, M. L.; Fagerstroem, C.-P.; Frisken, W. R.; Furutani, K. M.; Khakzad, M.; Schmidke, W. B.; ZEUS Collaboration

1995-02-01

Photoproduction at HERA is studied in ep collisions, with the ZEUS detector, for γp centre-of-mass energies ranging from 130-270 GeV. A sample of events with two high- pT jets ( pT > 6 GeV, η < 1.6) and a third cluster in the approximate direction of the electron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified as the photon remnant. Its properties, such as the transverse and longitudinal energy flows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the two jets in these events. The mean value of the photon remnant pT with respect to the beam axis is measured to be 2.1 ± 0.2 GeV, which demonstrates substantial mean transverse momenta for the photon remnant.

α-cluster versus non-α-cluster decay of the excited compound nucleus Ce124* using the dynamical cluster-decay model

NASA Astrophysics Data System (ADS)

Kaur, Arshdeep; Chopra, Sahila; Gupta, Raj K.

2014-03-01

The dynamical cluster-decay model (DCM), an extended version of the preformed cluster model (PCM) for ground-state (T =0) decays, is applied to study the decay of the proton-rich compound nucleus Ce124* formed in the S32 + Mo92 reaction at an above-barrier beam energy of 150 MeV. Application of the statistical code pace4 to experimental data shows large deviations in all cases of proton clusters' (2p, 3p, and 4p) evaporation residue (ER) and the non-α nucleus Be6 intermediate mass fragment (IMF). Furthermore, the α-nucleus Be8 decay is not observed in this experiment (not even the upper limit is given). Using the DCM, with effects of deformations up to hexadecapole and "compact" orientations included, for the best-fitted cross sections of 2p and 3p ERs and of Li5 and Be6 IMFs, the relative cross section of Be8 is found to be more than that of Be6, possibly due to the α-nucleus structure of Be8. The same is shown to be true for C12 versus C10, i.e., α-nuclei clusters are populated strongly relative to non-α clusters, similar to what was predicted by one of us (R.K.G.) et al. [S. Kumar, D. Bir, and R. K. Gupta, Phys. Rev. C 51, 1762 (1995), 10.1103/PhysRevC.51.1762] for ground-state decays of such nuclei and the decay of Ba116* formed in the Ni58 + Ni58 reaction at various compound nucleus excitation energies [R. K. Gupta et al., J. Phys. G: Nucl. Part. Phys. 32, 345 (2006), 10.1088/0954-3899/32/3/009]. The only parameter of the DCM is the neck-length ΔR, related to the "barrier-lowering" parameter. The compound nucleus formation probability and "barrier-lowering/-modification" effects are analyzed, and the role of varying the deformations of Be6 and/or Be8 nuclei on relative cross sections is studied, since the measured deformations are not available. The ones used here are from relativistic mean-field calculations [β2(6Be )=-0.087 and β2(8Be)=-0.094]. Calculations are also presented for a beam energy of 140 MeV, supporting the above result.

Examination of the nature of lattice matched III V semiconductor interfaces using computer simulated molecular beam epitaxial growth I. AC/BC interfaces

NASA Astrophysics Data System (ADS)

Thomsen, M.; Ghaisas, S. V.; Madhukar, A.

1987-07-01

A previously developed computer simulation of molecular beam epitaxial growth of III-V semiconductors based on the configuration dependent reactive incorporation (CDRI) model is extended to allow for two different cation species. Attention is focussed on examining the nature of interfaces formed in lattice matched quantum well structures of the form AC/BC/AC(100). We consider cation species with substantially different effective diffusion lengths, as is the case with Al and Ga during the growth of their respective As compounds. The degree of intermixing occuring at the interface is seen to be dependent upon, among other growth parameters, the pressure of the group V species during growth. Examination of an intraplanar order parameter at the interfaces reveals the existence of short range clustering of the cation species.

Correlation between structural and transport properties of electron beam irradiated PrMnO3 compounds

NASA Astrophysics Data System (ADS)

Christopher, Benedict; Rao, Ashok; Nagaraja, B. S.; Shyam Prasad, K.; Okram, G. S.; Sanjeev, Ganesh; Petwal, Vikash Chandra; Verma, Vijay Pal; Dwivedi, Jishnu; Poornesh, P.

2018-02-01

The structural, electrical, magnetic, and thermal properties of electron beam (EB) irradiated PrMnO3 manganites were investigated in the present communication. X-ray diffraction data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). Furthermore, the diffracted data are analyzed in detail using Rietveld refinement technique. It is observed that the EB dosage feebly disturbs the MnO6 octahedra. The electrical resistivity of all the samples exhibits semiconducting behavior. Small polaron hopping model is conveniently employed to investigate the semiconducting nature of the pristine as well as EB irradiated samples. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit large positive values at lower temperatures, signifying holes as the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism assists the thermoelectric transport property in the high temperature region. The magnetic measurements confirm the existence of paramagnetic (PM) to ferromagnetic (FM) behavior for the pristine and irradiated samples. In the lower temperature regime, coexistence of FM clusters and AFM matrix is dominating. Thus, the complex magnetic behavior of the compound has been explained in terms of rearrangement of antiferromagnetically coupled ionic moments.

Au3+ ion implantation on FTO coated glasses: Effect on structural, electrical, optical and phonon properties

NASA Astrophysics Data System (ADS)

Sahu, Bindu; Dey, Ranajit; Bajpai, P. K.

2017-06-01

Effects of 11.00 MeV Au3+ ions implanted in FTO coated (thickness ≈300 nm) silicate glasses on structural, electrical optical and phonon behavior have been explored. It has been observed that metal clustering near the surface and sub-surface region below glass-FTO interface changes electrical and optical properties significantly. Ion implantation does not affect the crystalline structure of the coated films; however, the unit cell volume decreases with increase in fluence and the tetragonal distortion (c/a ratio) also decreases systematically in the implanted samples. The sheet resistivity of the films increases from 11 × 10-5 ohm-cm (in pristine) to 7.5 × 10-4 ohm-cm for highest ion beam fluence ≈1015 ions/cm2. The optical absorption decreases with increasing fluence whereas, the optical transmittance as well as reflectance increases with increasing fluence. The Raman spectra are observed at ∼530 cm-1 and ∼1103 cm-1 in pristine sample. The broad band at 530 cm-1 shifts towards higher wave number in the irradiated samples. This may be correlated with increased disorder and strain relaxation in the samples as a result of ion beam irradiation.

Structure of 10Be and 16C nuclei via break-up reactions studied with the 4π Chimera array

NASA Astrophysics Data System (ADS)

Dell'Aquila, D.; Acosta, L.; Amorini, F.; Andolina, R.; Auditore, L.; Berceanu, I.; Cardella, G.; Chatterjiee, M. B.; De Filippo, E.; Francalanza, L.; Gnoffo, B.; Grzeszczuk, A.; Lanzalone, G.; Lombardo, I.; Martorana, N.; Minniti, T.; Pagano, A.; Pagano, E. V.; Papa, M.; Pirrone, S.; Politi, G.; Pop, A.; Porto, F.; Quattrocchi, L.; Rizzo, F.; Rosato, E.; Russotto, P.; Trifirò, A.; Trimarchi, M.; Verde, G.; Vigilante, M.

2018-01-01

The study of cluster states in neutron-rich Be and C isotopes is a subject of interest in Nuclear Physics. These states should be characterized by high deformation where α-clusters are bounded by valence neutrons. We performed a spectroscopic study of 10Be and 16C isotopes via projectile break-up reactions, by using radioactive beams produced at the INFN-LNS FRIBs facility and the Chimera 4π array. The possible evidence of a new 10Be state at 13.5 MeV excitation energy was found in the 6He+4He disintegration channel. The spectroscopy of 16C was studied via the 6He+10Be break-up channel; in this case we found the indication of a possible new state at about 20.6 MeV.

High-throughput shadow mask printing of passive electrical components on paper by supersonic cluster beam deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caruso, Francesco; Bellacicca, Andrea; Milani, Paolo, E-mail: pmilani@mi.infn.it

We report the rapid prototyping of passive electrical components (resistors and capacitors) on plain paper by an additive and parallel technology consisting of supersonic cluster beam deposition (SCBD) coupled with shadow mask printing. Cluster-assembled films have a growth mechanism substantially different from that of atom-assembled ones providing the possibility of a fine tuning of their electrical conduction properties around the percolative conduction threshold. Exploiting the precise control on cluster beam intensity and shape typical of SCBD, we produced, in a one-step process, batches of resistors with resistance values spanning a range of two orders of magnitude. Parallel plate capacitors withmore » paper as the dielectric medium were also produced with capacitance in the range of tens of picofarads. Compared to standard deposition technologies, SCBD allows for a very efficient use of raw materials and the rapid production of components with different shape and dimensions while controlling independently the electrical characteristics. Discrete electrical components produced by SCBD are very robust against deformation and bending, and they can be easily assembled to build circuits with desired characteristics. The availability of large batches of these components enables the rapid and cheap prototyping and integration of electrical components on paper as building blocks of more complex systems.« less

Fullerene formation and annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mintmire, J.W.

1996-04-05

Why does the highly symmetric carbon cluster C{sub 60} form in such profusion under the right conditions? This question was first asked in 1985, when Kroto suggested that the predominance of the C{sub 60} carbon clusters observed in the molecular beam experiments could be explained by the truncated icosahedral (or soccer ball) form. The name given to this cluster, buckminsterfullerene, led to the use of the term fullerenes for the family of hollow-cage carbon clusters made up of even numbers of triply coordinated carbons arranged with 12 pentagonal rings and an almost arbitrary number of hexagonal rings. More than amore » decade later, we still lack a completely satisfying understanding of the fundamental chemistry that takes place during fullerene formation. Most current models for fullerene formation require a facile mechanism for ring rearrangement in the fullerene structure, but the simplest proposed mechanisms are believed to have unrealistically high activation barriers. In recent research calculations have suggested that atomic carbon in the reaction mixture could act as a catalyst and allow substantially lower activation barriers for fullerene annealing. This article discusses the background for this research and other adjunct research. 14 refs.« less

High indium non-polar InGaN clusters with infrared sensitivity grown by PAMBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma

2015-03-15

Studies on the optical properties of InGaN alloy of relatively higher indium content are of potential interest to understand the effect of indium content on the optical band gap of epitaxial InGaN. We report the growth of self assembled non-polar high indium clusters of In{sub 0.55}Ga{sub 0.45}N over non-polar (11-20) a-plane In{sub 0.17}Ga{sub 0.83}N epilayer grown on a-plane (11-20)GaN/(1-102) r-plane sapphire substrate using plasma assisted molecular beam epitaxy (PAMBE). Such structures are potential candidates for high brightness LEDs emitting in longer wavelengths. The high resolution X-ray diffraction studies revealed the formation of two distinct compositions of In{sub x}Ga{sub 1−x}N alloys,more » which were further confirmed by photoluminescence studies. A possible mechanism for the formation of such structure was postulated which was supported with the results obtained by energy dispersive X-ray analysis. The structure hence grown when investigated for photo-detecting properties, showed sensitivity to both infrared and ultraviolet radiations due to the different composition of InGaN region.« less

Formation of metallic clusters in oxide insulators by means of ion beam mixing

NASA Astrophysics Data System (ADS)

Talut, G.; Potzger, K.; Mücklich, A.; Zhou, Shengqiang

2008-04-01

The intermixing and near-interface cluster formation of Pt and FePt thin films deposited on different oxide surfaces by means of Pt+ ion irradiation and subsequent annealing was investigated. Irradiated as well as postannealed samples were investigated using high resolution transmission electron microscopy. In MgO and Y :ZrO2 covered with Pt, crystalline clusters with mean sizes of 2 and 3.5nm were found after the Pt+ irradiations with 8×1015 and 2×1016cm-2 and subsequent annealing, respectively. In MgO samples covered with FePt, clusters with mean sizes of 1 and 2nm were found after the Pt+ irradiations with 8×1015 and 2×1016cm-2 and subsequent annealing, respectively. In Y :ZrO2 samples covered with FePt, clusters up to 5nm in size were found after the Pt+ irradiation with 2×1016cm-2 and subsequent annealing. In LaAlO3 the irradiation was accompanied by a full amorphization of the host matrix and appearance of embedded clusters of different sizes. The determination of the lattice constant and thus the kind of the clusters in samples covered by FePt was hindered due to strong deviation of the electron beam by the ferromagnetic FePt.

Supersonic Bare Metal Cluster Beams. Final Report

DOE R&D Accomplishments Database

Smalley, R. E.

1997-10-14

A major portion of the project involved elucidating the relation between reactivity and the electronic structure of transition-metal (TM) clusters of 2--200 atoms, which required the construction and continuous development of two principal apparati; the Fourier Transform-Ion Cyclotron Resonance (FT-ICR) apparatus, and Ultraviolet Photoelectron Spectroscopy (UPS). Together, these machines have enabled the most detailed probing of the structure and chemical reactivity of TM clusters. Clusters of all the transition metals were included in these studies. Fundamental aspects in chemisorption, reactivity, and heterogeneous catalysis have also become better understood as a result of these experiments for important classes of systems such as H{sub 2}, CO, and CO{sub 2} adsorbed onto clusters of many of the metals listed above. In particular, a correlation was found between reactivity of H{sub 2} with Fe, Co, and Ni clusters and differences between the cluster IP and EA. As recounted in a previous technical report, the DOE`s role in the initial discovery of fullerenes at Rice was central, and from the start investigations were made into metal atoms trapped in the fullerenes cage. More recently, the authors have discovered that 2--4 atoms of La, Y, or Sc can be produced by laser vaporization of composite graphite/metal-oxide disks. This work was largely motivated by the prospects of using such endohedral TM metals for their catalytic activity without the well-known difficulties of effective support media and lack of control over particle size. Thus, while it will certainly be important to discover ways to efficiently scale up production (e.g., the solar generation method explored with DOE support), the efforts have concentrated more on characterization, purification, and manipulation of doped fullerenes. For the past two years, much of the group`s effort has involved the production, purification, and characterization of carbon nanotubes.

Gas cluster ion beam surface treatments for reducing field emission and breakdown of electrodes and SRF cavities

NASA Astrophysics Data System (ADS)

Swenson, D. R.; Wu, A. T.; Degenkolb, E.; Insepov, Z.

2007-08-01

Sub-micron-scale surface roughness and contamination cause field emission that can lead to high-voltage breakdown of electrodes, and these are limiting factors in the development of high gradient RF technology. We are studying various Gas Cluster Ion Beam (GCIB) treatments to smooth, clean, etch and/or chemically alter electrode surfaces to allow higher fields and accelerating gradients, and to reduce the time and cost of conditioning high-voltage electrodes. For this paper, we have processed Nb, stainless steel and Ti electrode materials using beams of Ar, O2, or NF3 + O2 clusters with accelerating potentials up to 35 kV. Using a scanning field emission microscope (SFEM), we have repeatedly seen a dramatic reduction in the number of field emission sites on Nb coupons treated with GCIB. Smoothing effects on stainless steel and Ti substrates, evaluated using SEM and AFM imaging, show that 200-nm-wide polishing scratch marks are greatly attenuated. A 150-mm diameter GCIB-treated stainless steel electrode has shown virtually no DC field emission current at gradients over 20 MV/m.

STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF PET POLYMER FILMS MODIFIED BY LOW ENERGY Ar+ ION BEAMS

NASA Astrophysics Data System (ADS)

Fawzy, Y. H. A.; Abdel-Hamid, H. M.; El-Okr, M. M.; Atta, A.

Polyethylene terephthalate (PET) films with thickness 40μm are irradiated with 3keV argon ion beams with different fluence ranging from 0.5×1018ions.cm-2 to 2×1018ions.cm-2 using locally designed broad ion source. The changes in the PET structure are characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) techniques. The XRD patterns show that the peak intensity decreases with irradiation and the particle size decreases from 65.75 Å for the un-irradiated to 52.80 Å after irradiation. The FTIR indicates partial decrease and reduction in the intensity of the bands due to the degradation of the polymer after ion irradiation. The optical energy band gap decreases from 3.14eV to 3.05eV and the number of carbon cluster increases from 119 to 126 after ion irradiation. The results show a slight increase in the electrical conductivities and the dielectric constant (ɛ). The results indicate the effectiveness of using PET films as capacitors and resistors in industrial applications.

Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Dae-Kyu; Oh, Jeong-Do; Shin, Eun-Sol

2014-04-28

The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO{sub 2} dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage andmore » current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.« less

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

NASA Astrophysics Data System (ADS)

Crampton, Andrew S.; Rötzer, Marian D.; Ridge, Claron J.; Yoon, Bokwon; Schweinberger, Florian F.; Landman, Uzi; Heiz, Ueli

2016-10-01

The nature of the nano-catalyzed hydrogenation of ethylene, yielding benchmark information pertaining to the concept of structure sensitivity/insensitivity and its applicability at the bottom of the catalyst particle size-range, is explored with experiments on size-selected Ptn (n = 7-40) clusters soft-landed on MgO, in conjunction with first-principles simulations. As in the case of larger particles both the direct ethylene hydrogenation channel and the parallel hydrogenation-dehydrogenation ethylidyne-producing route must be considered, with the fundamental uncovering that at the < 1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to the structure insensitivity found for larger particles. In this size-regime, the chemical properties can be modulated and tuned by a single atom, reflected by the onset of low temperature hydrogenation at T > 150 K catalyzed by Ptn (n ≥ 10) clusters, with maximum room temperature reactivity observed for Pt13 using a pulsed molecular beam technique. Structure insensitive behavior, inherent for specific cluster sizes at ambient temperatures, can be induced in the more active sizes, e.g. Pt13, by a temperature increase, up to 400 K, which opens dehydrogenation channels leading to ethylidyne formation. This reaction channel was, however found to be attenuated on Pt20, as catalyst activity remained elevated after the 400 K step. Pt30 displayed behavior which can be understood from extrapolating bulk properties to this size range; in particular the calculated d-band center. In the non-scalable sub-nanometer size regime, however, precise control of particle size may be used for atom-by-atom tuning and manipulation of catalyzed hydrogenation activity and selectivity.

STATISTICALLY DETERMINED DISPERSION RELATIONS OF MAGNETIC FIELD FLUCTUATIONS IN THE TERRESTRIAL FORESHOCK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hnat, B.; O’Connell, D.; Nakariakov, V. M.

2016-08-20

We obtain dispersion relations of magnetic field fluctuations for two crossings of the terrestrial foreshock by Cluster spacecraft. These crossings cover plasma conditions that differ significantly in their plasma β and in the density of the reflected ion beam, but not in the properties of the encountered ion population, both showing shell-like distribution function. Dispersion relations are reconstructed using two-point instantaneous wave number estimations from pairs of Cluster spacecraft. The accessible range of wave vectors, limited by the available spacecraft separations, extends to ≈2 × 10{sup 4} km. Results show multiple branches of dispersion relations, associated with different powers ofmore » magnetic field fluctuations. We find that sunward propagating fast magnetosonic waves and beam resonant modes are dominant for the high plasma β interval with a dense beam, while the dispersions of the interval with low beam density include Alfvén and fast magnetosonic modes propagating sunward and anti-sunward.« less

Wideband Microstrip Antenna-Feeding Array

NASA Technical Reports Server (NTRS)

Huang, John

1990-01-01

Special impedance-matching probes help reduce feed complexity. Lightweight array of microstrip antenna elements designed to transmit and illuminate reflector antenna with circularly polarized radiation at 1,545 to 1,550 MHz and to receive circularly polarized radiation at 1,646 to 1,660 MHz. Microstrip array is cluster of 7 subarrays containing total of 28 microstrip patches. Produces cicularly polarized beam with suitable edge taper to illuminate reflector antenna. Teardrop-shaped feed probe provides gradual change of field from coaxial transmission line into microstrip substrate. Intended to be part of larger overlapping-cluster array generating multiple contiguous beams.

Terahertz imaging applied to cancer diagnosis.

PubMed

Brun, M-A; Formanek, F; Yasuda, A; Sekine, M; Ando, N; Eishii, Y

2010-08-21

We report on terahertz (THz) time-domain spectroscopy imaging of 10 microm thick histological sections. The sections are prepared according to standard pathological procedures and deposited on a quartz window for measurements in reflection geometry. Simultaneous acquisition of visible images enables registration of THz images and thus the use of digital pathology tools to investigate the links between the underlying cellular structure and specific THz information. An analytic model taking into account the polarization of the THz beam, its incidence angle, the beam shift between the reference and sample pulses as well as multiple reflections within the sample is employed to determine the frequency-dependent complex refractive index. Spectral images are produced through segmentation of the extracted refractive index data using clustering methods. Comparisons of visible and THz images demonstrate spectral differences not only between tumor and healthy tissues but also within tumors. Further visualization using principal component analysis suggests different mechanisms as to the origin of image contrast.

SU-E-T-314: The Application of Cloud Computing in Pencil Beam Scanning Proton Therapy Monte Carlo Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Z; Gao, M

Purpose: Monte Carlo simulation plays an important role for proton Pencil Beam Scanning (PBS) technique. However, MC simulation demands high computing power and is limited to few large proton centers that can afford a computer cluster. We study the feasibility of utilizing cloud computing in the MC simulation of PBS beams. Methods: A GATE/GEANT4 based MC simulation software was installed on a commercial cloud computing virtual machine (Linux 64-bits, Amazon EC2). Single spot Integral Depth Dose (IDD) curves and in-air transverse profiles were used to tune the source parameters to simulate an IBA machine. With the use of StarCluster softwaremore » developed at MIT, a Linux cluster with 2–100 nodes can be conveniently launched in the cloud. A proton PBS plan was then exported to the cloud where the MC simulation was run. Results: The simulated PBS plan has a field size of 10×10cm{sup 2}, 20cm range, 10cm modulation, and contains over 10,000 beam spots. EC2 instance type m1.medium was selected considering the CPU/memory requirement and 40 instances were used to form a Linux cluster. To minimize cost, master node was created with on-demand instance and worker nodes were created with spot-instance. The hourly cost for the 40-node cluster was $0.63 and the projected cost for a 100-node cluster was $1.41. Ten million events were simulated to plot PDD and profile, with each job containing 500k events. The simulation completed within 1 hour and an overall statistical uncertainty of < 2% was achieved. Good agreement between MC simulation and measurement was observed. Conclusion: Cloud computing is a cost-effective and easy to maintain platform to run proton PBS MC simulation. When proton MC packages such as GATE and TOPAS are combined with cloud computing, it will greatly facilitate the pursuing of PBS MC studies, especially for newly established proton centers or individual researchers.« less

Computational studies of small neutral vanadium oxide clusters and their reactions with sulfur dioxide

NASA Astrophysics Data System (ADS)

Jakubikova, Elena; He, Sheng-Gui; Xie, Yan; Matsuda, Yoshiyuki; Bernstein, Elliot

2007-03-01

Vanadium oxide is a catalytic system that plays an important role in the conversion of SO2 to SO3. Density functional theory at the BPW91/LANL2DZ level is employed to obtain structures of VOy (y=1,,5), V2Oy (y=2,,7), V3Oy (y=4,,9), V4Oy (y=7,,12) and their complexes with SO2. BPW91/LANL2DZ is insufficient to describe properly relative V-O and S-O bond strengths of vanadium and sulfur oxides. Calibration of theoretical results with experimental data is necessary to compute enthalpies of reactions between VxOy and SO2. Theoretical results indicate SO2 to SO conversion occurs for oxygen-deficient clusters and SO2 to SO3 conversion occurs for oxygen-rich clusters. Subsequent experimental studies confirm the presence of SO in the molecular beam as well as the presence of VxOy complexes with SO2. Some possible mechanisms for SO3 formation and catalyst regeneration for solids are also suggested.

Supramolecular clusters between carbohydrates and concave pyridines. Detection in the gas phase by resonance-enhanced multi-photon ionization reflectron time-of-flight mass spectrometer.

PubMed

Liebig, Timo; Lüning, Ulrich; Grotemeyer, Jürgen

2006-01-01

For the first time the formation of supramolecular clusters between concave pyridines and different carbohydrates could be observed in the gas phase. The different clusters have been investigated by means of laser desorption into a supersonic beam followed by resonant multi photon excitation yielding mass spectra with high intensity of the different cluster. These preliminary results open a way for the investigations of the hydrogen bonds in these compounds.

Performance of Multiplexed XY Resistive Micromegas detectors in a high intensity beam

NASA Astrophysics Data System (ADS)

Banerjee, D.; Burtsev, V.; Chumakov, A.; Cooke, D.; Depero, E.; Dermenev, A. V.; Donskov, S. V.; Dubinin, F.; Dusaev, R. R.; Emmenegger, S.; Fabich, A.; Frolov, V. N.; Gardikiotis, A.; Gninenko, S. N.; Hösgen, M.; Karneyeu, A. E.; Ketzer, B.; Kirsanov, M. M.; Konorov, I. V.; Kramarenko, V. A.; Kuleshov, S. V.; Levchenko, E.; Lyubovitskij, V. E.; Lysan, V.; Mamon, S.; Matveev, V. A.; Mikhailov, Yu. V.; Myalkovskiy, V. V.; Peshekhonov, V. D.; Peshekhonov, D. V.; Polyakov, V. A.; Radics, B.; Rubbia, A.; Samoylenko, V. D.; Tikhomirov, V. O.; Tlisov, D. A.; Toropin, A. N.; Vasilishin, B.; Arenas, G. Vasquez; Ulloa, P.; Crivelli, P.

2018-02-01

We present the performance of multiplexed XY resistive Micromegas detectors tested in the CERN SPS 100 GeV/c electron beam at intensities up to 3 . 3 × 105e- /(s ṡcm2) . So far, all studies with multiplexed Micromegas have only been reported for tests with radioactive sources and cosmic rays. The use of multiplexed modules in high intensity environments was not explored due to the effect of ambiguities in the reconstruction of the hit point caused by the multiplexing feature. For the specific mapping and beam intensities analyzed in this work with a multiplexing factor of five, more than 50% level of ambiguity is introduced due to particle pile-up as well as fake clusters due to the mapping feature. Our results prove that by using the additional information of cluster size and integrated charge from the signal clusters induced on the XY strips, the ambiguities can be reduced to a level below 2%. The tested detectors are used in the CERN NA64 experiment for tracking the incoming particles bending in a magnetic field in order to reconstruct their momentum. The average hit detection efficiency of each module was found to be ∼96% at the highest beam intensities. By using four modules a tracking resolution of 1.1% was obtained with ∼85% combined tracking efficiency.

Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization

PubMed Central

Vutova, Katia; Donchev, Veliko

2013-01-01

Computational modeling offers an opportunity for a better understanding and investigation of thermal transfer mechanisms. It can be used for the optimization of the electron beam melting process and for obtaining new materials with improved characteristics that have many applications in the power industry, medicine, instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR) is developed. The model predicts the change in the temperature field in the casting ingot during the interaction of the beam with the material. A modified Pismen-Rekford numerical scheme to discretize the analytical model is developed. These equation systems, describing the thermal processes and main characteristics of the developed numerical method, are presented. In order to optimize the technological regimes, different criteria for better refinement and obtaining dendrite crystal structures are proposed. Analytical problems of mathematical optimization are formulated, discretized and heuristically solved by cluster methods. Using important for the practice simulation results, suggestions can be made for EBMR technology optimization. The proposed tool is important and useful for studying, control, optimization of EBMR process parameters and improving of the quality of the newly produced materials. PMID:28788351

Inorganic material profiling using Arn+ cluster: Can we achieve high quality profiles?

NASA Astrophysics Data System (ADS)

Conard, T.; Fleischmann, C.; Havelund, R.; Franquet, A.; Poleunis, C.; Delcorte, A.; Vandervorst, W.

2018-06-01

Retrieving molecular information by sputtering of organic systems has been concretized in the last years due to the introduction of sputtering by large gas clusters which drastically eliminated the compound degradation during the analysis and has led to strong improvements in depth resolution. Rapidly however, a limitation was observed for heterogeneous systems where inorganic layers or structures needed to be profiled concurrently. As opposed to organic material, erosion of the inorganic layer appears very difficult and prone to many artefacts. To shed some light on these problems we investigated a simple system consisting of aluminum delta layer(s) buried in a silicon matrix in order to define the most favorable beam conditions for practical analysis. We show that counterintuitive to the small energy/atom used and unlike monoatomic ion sputtering, the information depth obtained with large cluster ions is typically very large (∼10 nm) and that this can be caused both by a large roughness development at early stages of the sputtering process and by a large mixing zone. As a consequence, a large deformation of the Al intensity profile is observed. Using sample rotation during profiling significantly improves the depth resolution while sample temperature has no significant effect. The determining parameter for high depth resolution still remains the total energy of the cluster instead of the energy per atom in the cluster.

Electron-induced chemistry in microhydrated sulfuric acid clusters

NASA Astrophysics Data System (ADS)

Lengyel, Jozef; Pysanenko, Andriy; Fárník, Michal

2017-11-01

We investigate the mixed sulfuric acid-water clusters in a molecular beam experiment with electron attachment and negative ion mass spectrometry and complement the experiment by density functional theory (DFT) calculations. The microhydration of (H2SO4)m(H2O)n clusters is controlled by the expansion conditions, and the electron attachment yields the main cluster ion series (H2SO4)m(H2O)nHSO4- and (H2O)nH2SO4-. The mass spectra provide an experimental evidence for the onset of the ionic dissociation of sulfuric acid and ion-pair (HSO4- ṡ ṡ ṡ H3O+) formation in the neutral H2SO4(H2O)n clusters with n ≥ 5 water molecules, in excellent agreement with the theoretical predictions. In the clusters with two sulfuric acid molecules (H2SO4)2(H2O)n this process starts as early as n ≥ 2 water molecules. The (H2SO4)m(H2O)nHSO4- clusters are formed after the dissociative electron attachment to the clusters containing the (HSO4- ṡ ṡ ṡ H3O+) ion-pair structure, which leads to the electron recombination with the H3O+ moiety generating H2O molecule and the H-atom dissociation from the cluster. The (H2O)nH2SO4- cluster ions point to an efficient caging of the H atom by the surrounding water molecules. The electron-energy dependencies exhibit an efficient electron attachment at low electron energies below 3 eV, and no resonances above this energy, for all the measured mass peaks. This shows that in the atmospheric chemistry only the low-energy electrons can be efficiently captured by the sulfuric acid-water clusters and converted into the negative ions. Possible atmospheric consequences of the acidic dissociation in the clusters and the electron attachment to the sulfuric acid-water aerosols are discussed.

Study of cluster shapes in a monolithic active pixel detector

NASA Astrophysics Data System (ADS)

Maçzewski, ł.; Adamus, M.; Ciborowski, J.; Grzelak, G.; łużniak, P.; Nieżurawski, P.; Żarnecki, A. F.

2009-11-01

Beamstrahlung will constitute an important source of background in a pixel vertex detector at the future International Linear Collider. Electron and positron tracks of this origin impact the pixel planes at angles generally larger than those of secondary hadrons and the corresponding clusters are elongated. We report studies of cluster characteristics using test beam electron tracks incident at various angles on a MIMOSA-5 monolithic active pixel sensor matrix.

Evaluation of biomolecular distributions in rat brain tissues by means of ToF-SIMS using a continuous beam of Ar clusters.

PubMed

Nakano, Shusuke; Yokoyama, Yuta; Aoyagi, Satoka; Himi, Naoyuki; Fletcher, John S; Lockyer, Nicholas P; Henderson, Alex; Vickerman, John C

2016-06-08

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) provides detailed chemical structure information and high spatial resolution images. Therefore, ToF-SIMS is useful for studying biological phenomena such as ischemia. In this study, in order to evaluate cerebral microinfarction, the distribution of biomolecules generated by ischemia was measured with ToF-SIMS. ToF-SIMS data sets were analyzed by means of multivariate analysis for interpreting complex samples containing unknown information and to obtain biomolecular mapping indicated by fragment ions from the target biomolecules. Using conventional ToF-SIMS (primary ion source: Bi cluster ion), it is difficult to detect secondary ions beyond approximately 1000 u. Moreover, the intensity of secondary ions related to biomolecules is not always high enough for imaging because of low concentration even if the masses are lower than 1000 u. However, for the observation of biomolecular distributions in tissues, it is important to detect low amounts of biological molecules from a particular area of tissue. Rat brain tissue samples were measured with ToF-SIMS (J105, Ionoptika, Ltd., Chandlers Ford, UK), using a continuous beam of Ar clusters as a primary ion source. ToF-SIMS with Ar clusters efficiently detects secondary ions related to biomolecules and larger molecules. Molecules detected by ToF-SIMS were examined by analyzing ToF-SIMS data using multivariate analysis. Microspheres (45 μm diameter) were injected into the rat unilateral internal carotid artery (MS rat) to cause cerebral microinfarction. The rat brain was sliced and then measured with ToF-SIMS. The brain samples of a normal rat and the MS rat were examined to find specific secondary ions related to important biomolecules, and then the difference between them was investigated. Finally, specific secondary ions were found around vessels incorporating microspheres in the MS rat. The results suggest that important biomolecules related to cerebral microinfarction can be detected by ToF-SIMS.

An Optical and Sunyaev-Zeldovich Blind Cluster Survey

NASA Astrophysics Data System (ADS)

Gomez, Percy; Romer, A. Kathy; Holzapfel, William; Peterson, Jeffrey; Ruhl, John; Goldstein, Jon; Daub, Mike

2005-08-01

We propose to perform multicolor observations of two deep fields that were observed with the ACBAR bolometer array located at the South Pole. These fields were observed down to a sensitivity of 8 microK/5 arcmin beam at 150 GHz. These observations will be used as control fields for our blind cluster survey which has identified some 30 cluster candidates to date. The goal of the observations is to quantify the number of clusters missed by our SZE survey. This information is important in order to derive constraints on sigma-8 from our SZE blind cluster survey.

MAPPER: high-throughput maskless lithography

NASA Astrophysics Data System (ADS)

Wieland, M. J.; de Boer, G.; ten Berge, G. F.; Jager, R.; van de Peut, T.; Peijster, J. J. M.; Slot, E.; Steenbrink, S. W. H. K.; Teepen, T. F.; van Veen, A. H. V.; Kampherbeek, B. J.

2009-03-01

Maskless electron beam lithography, or electron beam direct write, has been around for a long time in the semiconductor industry and was pioneered from the mid-1960s onwards. This technique has been used for mask writing applications as well as device engineering and in some cases chip manufacturing. However because of its relatively low throughput compared to optical lithography, electron beam lithography has never been the mainstream lithography technology. To extend optical lithography double patterning, as a bridging technology, and EUV lithography are currently explored. Irrespective of the technical viability of both approaches, one thing seems clear. They will be expensive [1]. MAPPER Lithography is developing a maskless lithography technology based on massively-parallel electron-beam writing with high speed optical data transport for switching the electron beams. In this way optical columns can be made with a throughput of 10-20 wafers per hour. By clustering several of these columns together high throughputs can be realized in a small footprint. This enables a highly cost-competitive alternative to double patterning and EUV alternatives. In 2007 MAPPER obtained its Proof of Lithography milestone by exposing in its Demonstrator 45 nm half pitch structures with 110 electron beams in parallel, where all the beams where individually switched on and off [2]. In 2008 MAPPER has taken a next step in its development by building several tools. The objective of building these tools is to involve semiconductor companies to be able to verify tool performance in their own environment. To enable this, the tools will have a 300 mm wafer stage in addition to a 110-beam optics column. First exposures at 45 nm half pitch resolution have been performed and analyzed. On the same wafer it is observed that all beams print and based on analysis of 11 beams the CD for the different patterns is within 2.2 nm from target and the CD uniformity for the different patterns is better than 2.8 nm.

High current H2(+) and H3(+) beam generation by pulsed 2.45 GHz electron cyclotron resonance ion source.

PubMed

Xu, Yuan; Peng, Shixiang; Ren, Haitao; Zhao, Jie; Chen, Jia; Zhang, Ailin; Zhang, Tao; Guo, Zhiyu; Chen, Jia'er

2014-02-01

The permanent magnet 2.45 GHz electron cyclotron resonance ion source at Peking University can produce more than 100 mA hydrogen ion beam working at pulsed mode. For the increasing requirements of cluster ions (H2(+) and H3(+)) in linac and cyclotron, experimental study was carried out to further understand the hydrogen plasma processes in the ion source for the generation of cluster ions. The constituents of extracted beam have been analyzed varying with the pulsed duration from 0.3 ms to 2.0 ms (repetition frequency 100 Hz) at different operation pressure. The fraction of cluster ions dramatically increased when the pulsed duration was lower than 0.6 ms, and more than 20 mA pure H3(+) ions with fraction 43.2% and 40 mA H2(+) ions with fraction 47.7% were obtained when the operation parameters were adequate. The dependence of extracted ion fraction on microwave power was also measured at different pressure as the energy absorbed by plasma will greatly influence electron temperature and electron density then the plasma processes in the ion source. More details will be presented in this paper.

Mapping Compound Cosmic Telescopes Containing Multiple Projected Cluster-scale Halos

NASA Astrophysics Data System (ADS)

Ammons, S. Mark; Wong, Kenneth C.; Zabludoff, Ann I.; Keeton, Charles R.

2014-01-01

Lines of sight with multiple projected cluster-scale gravitational lenses have high total masses and complex lens plane interactions that can boost the area of magnification, or étendue, making detection of faint background sources more likely than elsewhere. To identify these new "compound" cosmic telescopes, we have found directions in the sky with the highest integrated mass densities, as traced by the projected concentrations of luminous red galaxies (LRGs). We use new galaxy spectroscopy to derive preliminary magnification maps for two such lines of sight with total mass exceeding ~3 × 1015 M ⊙. From 1151 MMT Hectospec spectra of galaxies down to i AB = 21.2, we identify two to three group- and cluster-scale halos in each beam. These are well traced by LRGs. The majority of the mass in beam J085007.6+360428 (0850) is contributed by Zwicky 1953, a massive cluster at z = 0.3774, whereas beam J130657.5+463219 (1306) is composed of three halos with virial masses of 6 × 1014-2 × 1015 M ⊙, one of which is A1682. The magnification maps derived from our mass models based on spectroscopy and Sloan Digital Sky Survey photometry alone display substantial étendue: the 68% confidence bands on the lens plane area with magnification exceeding 10 for a source plane of zs = 10 are [1.2, 3.8] arcmin2 for 0850 and [2.3, 6.7] arcmin2 for 1306. In deep Subaru Suprime-Cam imaging of beam 0850, we serendipitously discover a candidate multiply imaged V-dropout source at z phot = 5.03. The location of the candidate multiply imaged arcs is consistent with the critical curves for a source plane of z = 5.03 predicted by our mass model. Incorporating the position of the candidate multiply imaged galaxy as a constraint on the critical curve location in 0850 narrows the 68% confidence band on the lens plane area with μ > 10 and zs = 10 to [1.8, 4.2] arcmin2, an étendue range comparable to that of MACS 0717+3745 and El Gordo, two of the most powerful single cluster lenses known. The significant lensing power of our beams makes them powerful probes of reionization and galaxy formation in the early universe.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laskin, Julia; Johnson, Grant E.; Prabhakaran, Venkateshkumar

Immobilization of complex molecules and clusters on supports plays an important role in a variety of disciplines including materials science, catalysis and biochemistry. In particular, deposition of clusters on surfaces has attracted considerable attention due to their non-scalable, highly size-dependent properties. The ability to precisely control the composition and morphology of clusters and small nanoparticles on surfaces is crucial for the development of next generation materials with rationally tailored properties. Soft- and reactive landing of ions onto solid or liquid surfaces introduces unprecedented selectivity into surface modification by completely eliminating the effect of solvent and sample contamination on the qualitymore » of the film. The ability to select the mass-to-charge ratio of the precursor ion, its kinetic energy and charge state along with precise control of the size, shape and position of the ion beam on the deposition target makes soft-landing an attractive approach for surface modification. High-purity uniform thin films on surfaces generated using mass-selected ion deposition facilitate understanding of critical interfacial phenomena relevant to catalysis, energy generation and storage, and materials science. Our efforts have been directed toward understanding charge retention by soft-landed metal and metal-oxide cluster ions, which may affect both their structure and reactivity. Specifically, we have examined the effect of the surface on charge retention by both positively and negatively charged cluster ions. We found that the electronic properties of the surface play an important role in charge retention by cluster cations. Meanwhile, the electron binding energy is a key factor determining charge retention by cluster anions. These findings provide the scientific foundation for the rational design of interfaces for advanced catalysts and energy storage devices. Further optimization of electrode-electrolyte interfaces for applications in energy storage and electrocatalysis may be achieved by understanding and controlling the properties of soft-landed cluster ions.« less

A multi-point perspective on the formation of polar cap arcs: kinetic modeling and observations by Cluster and TIMED

NASA Astrophysics Data System (ADS)

de Keyser, J. M.; Maggiolo, R.; Echim, M.; Simon, C.; Zhang, Y.; Trotignon, J.

2010-12-01

On April 1st, 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. Simultaneously, the Cluster spacecraft detects an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 600 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 300eV. The footprint of the magnetic field line on which the Cluster spacecraft are situated, is located just outside the GUVI field of view in the prolongation of the polar cap arc. This suggests that the upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at ionospheric altitudes corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The energy spectrum of the precipitating electrons provided by the model is introduced as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes like photoionisation and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are then compared to the optical observations by TIMED. Data and modeling results are consistent with quasi-static acceleration of precipitating magnetospheric electrons. We also discuss possible implications of our modeling results for optical observations of polar cap arcs.

Electron beam diagnostic system using computed tomography and an annular sensor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmer, John W.; Teruya, Alan T.

2015-08-11

A system for analyzing an electron beam including a circular electron beam diagnostic sensor adapted to receive the electron beam, the circular electron beam diagnostic sensor having a central axis; an annular sensor structure operatively connected to the circular electron beam diagnostic sensor, wherein the sensor structure receives the electron beam; a system for sweeping the electron beam radially outward from the central axis of the circular electron beam diagnostic sensor to the annular sensor structure wherein the electron beam is intercepted by the annular sensor structure; and a device for measuring the electron beam that is intercepted by themore » annular sensor structure.« less

Electron beam diagnostic system using computed tomography and an annular sensor

DOEpatents

Elmer, John W.; Teruya, Alan T.

2014-07-29

A system for analyzing an electron beam including a circular electron beam diagnostic sensor adapted to receive the electron beam, the circular electron beam diagnostic sensor having a central axis; an annular sensor structure operatively connected to the circular electron beam diagnostic sensor, wherein the sensor structure receives the electron beam; a system for sweeping the electron beam radially outward from the central axis of the circular electron beam diagnostic sensor to the annular sensor structure wherein the electron beam is intercepted by the annular sensor structure; and a device for measuring the electron beam that is intercepted by the annular sensor structure.

XPS investigation of depth profiling induced chemistry

NASA Astrophysics Data System (ADS)

Pratt, Quinn; Skinner, Charles; Koel, Bruce; Chen, Zhu

2017-10-01

Surface analysis is an important tool for understanding plasma-material interactions. Depth profiles are typically generated by etching with a monatomic argon ion beam, however this can induce unintended chemical changes in the sample. Tantalum pentoxide, a sputtering standard, and PEDOT:PSS, a polymer that was used to mimic the response of amorphous carbon-hydrogen co-deposits, were studied. We compare depth profiles generated with monatomic and gas cluster argon ion beams (GCIB) using X-ray photoelectron spectroscopy (XPS) to quantify chemical changes. In both samples, monatomic ion bombardment led to beam-induced chemical changes. Tantalum pentoxide exhibited preferential sputtering of oxygen and the polymer experienced significant bond modification. Depth profiling with clusters is shown to mitigate these effects. We present sputtering rates for Ta2O5 and PEDOT:PSS as a function of incident energy and flux. Support was provided through DOE Contract Number DE-AC02-09CH11466.

Mechanical and microstructural changes in tungsten due to irradiation damage

NASA Astrophysics Data System (ADS)

Uytdenhouwen, I.; Schwarz-Selinger, T.; Coenen, J. W.; Wirtz, M.

2016-02-01

Stress-relieved pure tungsten received three damage levels (0.10, 0.25 and 0.50 dpa) by self-tungsten ion beam irradiation at room temperature. Positron annihilation spectroscopy showed the formation of mono-vacancies and vacancy clusters after ion beam exposure. In the first irradiation step (0-0.10 dpa) some splitting up of large vacancy clusters occurred which became more numerous. For increasing dose to 0.25 dpa, growth of the vacancy clusters was seen. At 0.50 dpa a change in the defect formation seems to occur leading to a saturation in the lifetime signal obtained from the positrons. Nano-indentation on the cross-sections showed a flat damage depth distribution profile. The nano-indentation hardness increased for increasing damage dose without any saturation up to 0.50 dpa. This means that other defects such as dislocation loops and large sized voids seem to contribute.

Stretchable nanocomposite electrodes with tunable mechanical properties by supersonic cluster beam implantation in elastomers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borghi, F.; Podestà, A.; Milani, P., E-mail: pmilani@mi.infn.it

We demonstrate the fabrication of gold-polydimethylsiloxane nanocomposite electrodes, by supersonic cluster beam implantation, with tunable Young's modulus depending solely on the amount of metal clusters implanted in the elastomeric matrix. We show both experimentally and by atomistic simulations that the mechanical properties of the nanocomposite can be maintained close to that of the bare elastomer for significant metal volume concentrations. Moreover, the elastic properties of the nanocomposite, as experimentally characterized by nanoindentation and modeled with molecular dynamics simulations, are also well described by the Guth-Gold classical model for nanoparticle-filled rubbers, which depends on the presence, concentration, and aspect ratio ofmore » metal nanoparticles, and not on the physical and chemical modification of the polymeric matrix due to the embedding process. The elastic properties of the nanocomposite can therefore be determined and engineered a priori, by controlling only the nanoparticle concentration.« less

Evaluation of clustering algorithms at the < 1 GeV energy scale for the electromagnetic calorimeter of the PADME experiment

NASA Astrophysics Data System (ADS)

Leonardi, E.; Piperno, G.; Raggi, M.

2017-10-01

A possible solution to the Dark Matter problem postulates that it interacts with Standard Model particles through a new force mediated by a “portal”. If the new force has a U(1) gauge structure, the “portal” is a massive photon-like vector particle, called dark photon or A’. The PADME experiment at the DAΦNE Beam-Test Facility (BTF) in Frascati is designed to detect dark photons produced in positron on fixed target annihilations decaying to dark matter (e+e-→γA‧) by measuring the final state missing mass. One of the key roles of the experiment will be played by the electromagnetic calorimeter, which will be used to measure the properties of the final state recoil γ. The calorimeter will be composed by 616 21×21×230 mm3 BGO crystals oriented with the long axis parallel to the beam direction and disposed in a roughly circular shape with a central hole to avoid the pile up due to the large number of low angle Bremsstrahlung photons. The total energy and position of the electromagnetic shower generated by a photon impacting on the calorimeter can be reconstructed by collecting the energy deposits in the cluster of crystals interested by the shower. In PADME we are testing two different clustering algorithms, PADME-Radius and PADME-Island, based on two complementary strategies. In this paper we will describe the two algorithms, with the respective implementations, and report on the results obtained with them at the PADME energy scale (< 1 GeV), both with a GEANT4 based simulation and with an existing 5×5 matrix of BGO crystals tested at the DAΦNE BTF.

Investigation of Metal and Metal Oxide Clusters Small Enough to Constitute the Critical Size for Gas Phase Nucleation in Combustion Processes.

DTIC Science & Technology

1980-11-01

Ao-A093 950 NORTHWESTERN UNIV EVANSTON IL DEPT OF M4ECHANICAL ND-ETC F/S 7/4 INVESTIGATION OF 1ETAL AND METAL OXIDE CLUSTERS S1ALL ENOUGH TO--ETC(U...34 " 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue on reveroe side if necessary snd Identify by block number) Clusters , Nucleation, Molecular Beam, Free...contract a variety of techniques have been employed to study the properties of small atomic and molecular clusters formed in the gas phase via

Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD

NASA Astrophysics Data System (ADS)

Pickett, J. S.; Chen, L.-J.; Santolík, O.; Grimald, S.; Lavraud, B.; Verkhoglyadova, O. P.; Tsurutani, B. T.; Lefebvre, B.; Fazakerley, A.; Lakhina, G. S.; Ghosh, S. S.; Grison, B.; Décréau, P. M. E.; Gurnett, D. A.; Torbert, R.; Cornilleau-Wehrlin, N.; Dandouras, I.; Lucek, E.

2009-06-01

Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 RE and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2) the EDI instrument detected bursts of field-aligned electron currents, 3) the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4) the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5) CIS detected nearly comparable densities of H+ and O+ ions and a large tailward H+ velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD) with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in more detail using the space measurements as inputs to models, and better relate the ESW space measurements to the laboratory through PIC code models.

Hybrid Organic/Inorganic Materials Depth Profiling Using Low Energy Cesium Ions

NASA Astrophysics Data System (ADS)

Noël, Céline; Houssiau, Laurent

2016-05-01

The structures developed in organic electronics, such as organic light emitting diodes (OLEDs) or organic photovoltaics (OPVs) devices always involve hybrid interfaces, joining metal or oxide layers with organic layers. No satisfactory method to probe these hybrid interfaces physical chemistry currently exists. One promising way to analyze such interfaces is to use in situ ion beam etching, but this requires ion beams able to depth profile both inorganic and organic layers. Mono- or diatomic ion beams commonly used to depth profile inorganic materials usually perform badly on organics, while cluster ion beams perform excellently on organics but yield poor results when organics and inorganics are mixed. Conversely, low energy Cs+ beams (<500 eV) allow organic and inorganic materials depth profiling with comparable erosion rates. This paper shows a successful depth profiling of a model hybrid system made of metallic (Au, Cr) and organic (tyrosine) layers, sputtered with 500 eV Cs+ ions. Tyrosine layers capped with metallic overlayers are depth profiled easily, with high intensities for the characteristic molecular ions and other specific fragments. Metallic Au or Cr atoms are recoiled into the organic layer where they cause some damage near the hybrid interface as well as changes in the erosion rate. However, these recoil implanted metallic atoms do not appear to severely degrade the depth profile overall quality. This first successful hybrid depth profiling report opens new possibilities for the study of OLEDs, organic solar cells, or other hybrid devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Woo-Young; Seol, Jae-Bok, E-mail: jb-seol@postech.ac.kr; Kwak, Chan-Min

The compositional distribution of In atoms in InGaN/GaN multiple quantum wells is considered as one of the candidates for carrier localization center, which enhances the efficiency of the light-emitting diodes. However, two challenging issues exist in this research area. First, an inhomogeneous In distribution is initially formed by spinodal decomposition during device fabrication as revealed by transmission electron microscopy. Second, electron-beam irradiation during microscopy causes the compositional inhomogeneity of In to appear as a damage contrast. Here, a systematic approach was proposed in this study: Electron-beam with current density ranging from 0 to 20.9 A/cm{sup 2} was initially exposed to themore » surface regions during microscopy. Then, the electron-beam irradiated regions at the tip surface were further removed, and finally, atom probe tomography was performed to run the samples without beam-induced damage and to evaluate the existence of local inhomegenity of In atoms. We proved that after eliminating the electron-beam induced damage regions, no evidence of In clustering was observed in the blue-emitting InGaN/GaN devices. In addition, it is concluded that the electron-beam induced localization of In atoms is a surface-related phenomenon, and hence spinodal decomposition, which is typically responsible for such In clustering, is negligible for biaxially strained blue-emitting InGaN/GaN devices.« less

Non-Abelian Bremsstrahlung and Azimuthal Asymmetries in High Energy p+A Reactions

DOE PAGES

Gyulassy, Miklos; Vitev, Ivan Mateev; Levai, Peter; ...

2014-09-25

Here we apply the GLV reaction operator solution to the Vitev-Gunion-Bertsch (VGB) boundary conditions to compute the all-order in nuclear opacity non-abelian gluon bremsstrahlung of event- by-event uctuating beam jets in nuclear collisions. We evaluate analytically azimuthal Fourier moments of single gluon, vmore » $$M\\atop{n}$$ {1}, and even number 2ℓ gluon, v$$M\\atop{n}$$ {2ℓ} inclusive distributions in high energy p+A reactions as a function of harmonic $n$, target recoil cluster number, $M$, and gluon number, 2ℓ, at RHIC and LHC. Multiple resolved clusters of recoiling target beam jets together with the projectile beam jet form Color Scintillation Antenna (CSA) arrays that lead to character- istic boost non-invariant trapezoidal rapidity distributions in asymmetric B+A nuclear collisions. The scaling of intrinsically azimuthally anisotropic and long range in η nature of the non-Abelian bremsstrahlung leads to v n moments that are similar to results from hydrodynamic models, but due entirely to non-Abelian wave interference phenomena sourced by the fluctuating CSA. Our analytic non-flow solutions are similar to recent numerical saturation model predictions but differ by predicting a simple power-law hierarchy of both even and odd v n without invoking k T factorization. A test of CSA mechanism is the predicted nearly linear η rapidity dependence of the v n(k Tη). Non- Abelian beam jet bremsstrahlung may thus provide a simple analytic solution to Beam Energy Scan (BES) puzzle of the near $$\\sqrt{s}$$ independence of v n(pT) moments observed down to 10 AGeV where large-x valence quark beam jets dominate inelastic dynamics. Recoil bremsstrahlung from multiple independent CSA clusters could also provide a partial explanation for the unexpected similarity of v n in p(D) + A and non-central A + A at same dN=dη multiplicity as observed at RHIC and LHC.« less

Melting of isolated tin nanoparticles

PubMed

Bachels; Guntherodt; Schafer

2000-08-07

The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

ON THE CLUSTERING OF SUBMILLIMETER GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Christina C.; Giavalisco, Mauro; Yun, Min S.

2011-06-01

We measure the angular two-point correlation function of submillimeter galaxies (SMGs) from 1.1 mm imaging of the COSMOS field with the AzTEC camera and ASTE 10 m telescope. These data yield one of the largest contiguous samples of SMGs to date, covering an area of 0.72 deg{sup 2} down to a 1.26 mJy beam{sup -1} (1{sigma}) limit, including 189 (328) sources with S/N {>=}3.5 (3). We can only set upper limits to the correlation length r{sub 0}, modeling the correlation function as a power law with pre-assigned slope. Assuming existing redshift distributions, we derive 68.3% confidence level upper limits ofmore » r{sub 0} {approx}< 6-8h{sup -1} Mpc at 3.7 mJy and r{sub 0} {approx}< 11-12 h{sup -1} Mpc at 4.2 mJy. Although consistent with most previous estimates, these upper limits imply that the real r{sub 0} is likely smaller. This casts doubts on the robustness of claims that SMGs are characterized by significantly stronger spatial clustering (and thus larger mass) than differently selected galaxies at high redshift. Using Monte Carlo simulations we show that even strongly clustered distributions of galaxies can appear unclustered when sampled with limited sensitivity and coarse angular resolution common to current submillimeter surveys. The simulations, however, also show that unclustered distributions can appear strongly clustered under these circumstances. From the simulations, we predict that at our survey depth, a mapped area of 2 deg{sup 2} is needed to reconstruct the correlation function, assuming smaller beam sizes of future surveys (e.g., the Large Millimeter Telescope's 6'' beam size). At present, robust measures of the clustering strength of bright SMGs appear to be below the reach of most observations.« less

Laser microprocessing and nanoengineering of large-area functional micro/nanostructures

NASA Astrophysics Data System (ADS)

Tang, M.; Xie, X. Z.; Yang, J.; Chen, Z. C.; Xu, L.; Choo, Y. S.; Hong, M. H.

2011-12-01

Laser microprocessing and nanoengineering are of great interest to both scientists and engineers, since the inspired properties of functional micro/nanostructures over large areas can lead to numerous unique applications. Currently laser processing systems combined with high speed automation ensure the focused laser beam to process various materials at a high throughput and a high accuracy over large working areas. UV lasers are widely used in both laser microprocessing and nanoengineering. However by improving the processing methods, green pulsed laser is capable of replacing UV lasers to make high aspect ratio micro-grooves on fragile and transparent sapphire substrates. Laser micro-texturing can also tune the wetting property of metal surfaces from hydrophilic to super-hydrophobic at a contact angle of 161° without chemical coating. Laser microlens array (MLA) can split a laser beam into multiple laser beams and reduce the laser spot size down to sub-microns. It can be applied to fabricate split ring resonator (SRR) meta-materials for THz sensing, surface plasmonic resonance (SPR) structures for NIR and molding tools for soft lithography. Furthermore, laser interference lithography combined with thermal annealing can obtain a large area of sub-50nm nano-dot clusters used for SPR applications.

Electronic structure and charge transport in nonstoichiometric tantalum oxide

NASA Astrophysics Data System (ADS)

Perevalov, T. V.; Gritsenko, V. A.; Gismatulin, A. A.; Voronkovskii, V. A.; Gerasimova, A. K.; Aliev, V. Sh; Prosvirin, I. A.

2018-06-01

The atomic and electronic structure of nonstoichiometric oxygen-deficient tantalum oxide TaO x<2.5 grown by ion beam sputtering deposition was studied. The TaO x film content was analyzed by x-ray photoelectron spectroscopy and by quantum-chemistry simulation. TaO x is composed of Ta2O5, metallic tantalum clusters and tantalum suboxides. A method for evaluating the stoichiometry parameter of TaO x from the comparison of experimental and theoretical photoelectron valence band spectra is proposed. The charge transport properties of TaO x were experimentally studied and the transport mechanism was quantitatively analyzed with four theoretical dielectric conductivity models. It was found that the charge transport in almost stoichiometric and nonstoichiometric tantalum oxide can be consistently described by the phonon-assisted tunneling between traps.

Development of III-nitride semiconductors by molecular beam epitaxy and cluster beam epitaxy and fabrication of LEDs based on indium gallium nitride MQWs

NASA Astrophysics Data System (ADS)

Chen, Tai-Chou Papo

The family of III-Nitrides (the binaries InN, GaN, AIN, and their alloys) is one of the most important classes of semiconductor materials. Of the three, Indium Nitride (InN) and Aluminum Nitride (AIN) have been investigated much less than Gallium Nitride (GaN). However, both of these materials are important for optoelectronic infrared and ultraviolet devices. In particular, since InN was found recently to be a narrow gap semiconductor (Eg=0.7eV), its development should extend the applications of nitride semiconductors to the spectral region appropriate to fiber optics communication and photovoltaic applications. Similarly, the development of AIN should lead to deep UV light emitting diodes (LEDs). The first part of this work addresses the evaluation of structural, optical and transport properties of InN films grown by two different deposition methods. In one method, active nitrogen was produced in the form of nitrogen radicals by a radio frequency (RF) plasma-assisted source. In an alternative method, active nitrogen was produced in the form of clusters containing approximately 2000 nitrogen molecules. These clusters were produced by adiabatic expansion from high stagnation pressure through a narrow nozzle into vacuum. The clusters were singly or doubly ionized with positive charge by electron impact and accelerated up to approximately 20 to 25 KV prior to their disintegration on the substrate. Due to the high local temperature produced during the impact of clusters with the substrate, this method is suitable for the deposition of InN at very low temperatures. The films are auto-doped n-type with carrier concentrations varying from 3 x 1018 to 1020 cm-3 and the electron effective mass of these films was determined to be 0.09m0. The majority of the AIN films was grown by the cluster beam epitaxy method and was doped n- and p- type by incorporating silicon (Si) and magnesium (Mg) during the film deposition. All films were grown under Al-rich conditions at relatively high temperatures (800˜1050°C) in order to increase the solubility of nitrogen into the free Al on the surface of the growing film. The films were found to have smooth surface morphology with narrow on-axis X-ray diffraction (XRD) rocking curves and relatively broad off-axis XRD rocking curves attributed to the lack of a buffer layer during the film growth. The device aspect of this work involves the material formation and the device fabrication of Indium Gallium Nitride (InGaN) based LEDs on textured GaN templates produced spontaneously by either hydride vapor phase epitaxy (HVPE) or using a method of natural lithography and reactive ion etching. This part of the work includes the film deposition and characterization of InGaNJGaN quantum wells on smooth and textured GaN template.

Interplay of weak interactions in the atom-by-atom condensation of xenon within quantum boxes

PubMed Central

Nowakowska, Sylwia; Wäckerlin, Aneliia; Kawai, Shigeki; Ivas, Toni; Nowakowski, Jan; Fatayer, Shadi; Wäckerlin, Christian; Nijs, Thomas; Meyer, Ernst; Björk, Jonas; Stöhr, Meike; Gade, Lutz H.; Jung, Thomas A.

2015-01-01

Condensation processes are of key importance in nature and play a fundamental role in chemistry and physics. Owing to size effects at the nanoscale, it is conceptually desired to experimentally probe the dependence of condensate structure on the number of constituents one by one. Here we present an approach to study a condensation process atom-by-atom with the scanning tunnelling microscope, which provides a direct real-space access with atomic precision to the aggregates formed in atomically defined ‘quantum boxes’. Our analysis reveals the subtle interplay of competing directional and nondirectional interactions in the emergence of structure and provides unprecedented input for the structural comparison with quantum mechanical models. This approach focuses on—but is not limited to—the model case of xenon condensation and goes significantly beyond the well-established statistical size analysis of clusters in atomic or molecular beams by mass spectrometry. PMID:25608225

Study of the bending vibration characteristic of phononic crystals beam-foundation structures by Timoshenko beam theory

NASA Astrophysics Data System (ADS)

Zhang, Yan; Ni, Zhi-Qiang; Jiang, Lin-Hua; Han, Lin; Kang, Xue-Wei

2015-07-01

Vibration problems wildly exist in beam-foundation structures. In this paper, finite periodic composites inspired by the concept of ideal phononic crystals (PCs), as well as Timoshenko beam theory (TBT), are proposed to the beam anchored on Winkler foundation. The bending vibration band structure of the PCs Timoshenko beam-foundation structure is derived from the modified transfer matrix method (MTMM) and Bloch's theorem. Then, the frequency response of the finite periodic composite Timoshenko beam-foundation structure by the finite element method (FEM) is performed to verify the above theoretical deduction. Study shows that the Timoshenko beam-foundation structure with periodic composites has wider attenuation zones compared with homogeneous ones. It is concluded that TBT is more available than Euler beam theory (EBT) in the study of the bending vibration characteristic of PCs beam-foundation structures with different length-to-height ratios.

Optical signatures of molecular particles via mass-selected cluster spectroscopy

NASA Technical Reports Server (NTRS)

Duncan, Michael A.

1990-01-01

A new molecular beam apparatus was developed to study optical absorption in cold (less than 100 K) atomic clusters and complexes produced by their condensation with simple molecular gases. In this instrument, ionized clusters produced in a laser vaporization nozzle source are mass selected and studied with photodissociation spectroscopy at visible and ultraviolet wavelengths. This new approach can be applied to synthesize and characterize numerous particulates and weakly bound complexes expected in planetary atmospheres and in comets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jie; He, Yunteng; Kong, Wei, E-mail: wei.kong@oregonstate.edu

We report electron diffraction of ferrocene doped in superfluid helium droplets. By taking advantage of the velocity slip in our pulsed droplet beam using a pulsed electron gun, and by doping with a high concentration of ferrocene delivered via a pulsed valve, we can obtain high quality diffraction images from singly doped droplets. Under the optimal doping conditions, 80% of the droplets sampled in the electron beam are doped with just one ferrocene molecule. Extension of this size selection method to dopant clusters has also been demonstrated. However, incomplete separation of dopant clusters might require deconvolution and modeling of themore » doping process. This method can be used for studies of nucleation processes in superfluid helium droplets.« less

Measuring the density of a molecular cluster injector via visible emission from an electron beam.

PubMed

Lundberg, D P; Kaita, R; Majeski, R; Stotler, D P

2010-10-01

A method to measure the density distribution of a dense hydrogen gas jet is presented. A Mach 5.5 nozzle is cooled to 80 K to form a flow capable of molecular cluster formation. A 250 V, 10 mA electron beam collides with the jet and produces H(α) emission that is viewed by a fast camera. The high density of the jet, several 10(16) cm(-3), results in substantial electron depletion, which attenuates the H(α) emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

On atomic structure of Ge huts growing on the Ge/Si(001) wetting layer

NASA Astrophysics Data System (ADS)

Arapkina, Larisa V.; Yuryev, Vladimir A.

2013-09-01

Structural models of growing Ge hut clusters—pyramids and wedges—are proposed on the basis of data of recent STM investigations of nucleation and growth of Ge huts on the Si(001) surface in the process of molecular beam epitaxy. It is shown that extension of a hut base along ⟨110⟩ directions goes non-uniformly during the cluster growth regardless of its shape. Growing pyramids, starting from the second monolayer, pass through cyclic formation of slightly asymmetrical and symmetrical clusters, with symmetrical ones appearing after addition of every fourth monolayer. We suppose that pyramids of symmetrical configurations composed by 2, 6, 10, etc., monolayers over the wetting layer are more stable than asymmetrical ones. This might explain less stability of pyramids in comparison with wedges in dense arrays forming at low temperatures of Ge deposition. Possible nucleation processes of pyramids and wedges on wetting layer patches from identical embryos composed by 8 dimers through formation of 1 monolayer high 16-dimer nuclei different only in their symmetry is discussed. Schematics of these processes are presented. It is concluded from precise STM measurements that top layers of wetting layer patches are relaxed when huts nucleate on them.

On atomic structure of Ge huts growing on the Ge/Si(001) wetting layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arapkina, Larisa V.; Yuryev, Vladimir A.

Structural models of growing Ge hut clusters—pyramids and wedges—are proposed on the basis of data of recent STM investigations of nucleation and growth of Ge huts on the Si(001) surface in the process of molecular beam epitaxy. It is shown that extension of a hut base along <110> directions goes non-uniformly during the cluster growth regardless of its shape. Growing pyramids, starting from the second monolayer, pass through cyclic formation of slightly asymmetrical and symmetrical clusters, with symmetrical ones appearing after addition of every fourth monolayer. We suppose that pyramids of symmetrical configurations composed by 2, 6, 10, etc., monolayersmore » over the wetting layer are more stable than asymmetrical ones. This might explain less stability of pyramids in comparison with wedges in dense arrays forming at low temperatures of Ge deposition. Possible nucleation processes of pyramids and wedges on wetting layer patches from identical embryos composed by 8 dimers through formation of 1 monolayer high 16-dimer nuclei different only in their symmetry is discussed. Schematics of these processes are presented. It is concluded from precise STM measurements that top layers of wetting layer patches are relaxed when huts nucleate on them.« less

Mechanisms of Diagonal-Shear Failure in Reinforced Concrete Beams analyzed by AE-SiGMA

NASA Astrophysics Data System (ADS)

Ohno, Kentaro; Shimozono, Shinichiro; Sawada, Yosuke; Ohtsu, Masayasu

Serious shear failures in reinforced concrete (RC) structures were reported in the Hanshin-Awaji Earthquake. In particular, it was demonstrated that a diagonal-shear failure could lead to disastrous damage. However, mechanisms of the diagonal-shear failure in RC beams have not been completely clarified yet. In this study, the diagonal-shear failure in RC beams is investigated, applying acoustic emission (AE) method. To identify source mechanisms of AE signals, SiGMA (Simplified Green's functions for Moment tensor Analysis) procedure was applied. Prior to four-point bending tests of RC beams, theoretical waveforms were calculated to determine the optimal arrangement of AE sensors. Then, cracking mechanisms in experiments were investigated by applying the SiGMA procedure to AE waveforms. From results of the SiGMA analysis, dominant motions of micro-cracks are found to be of shear crack in all the loading stages. As the load increased, the number of tensile cracks increased and eventually the diagonal-shear failure occurred in the shear span. Prior to final failure, AE cluster of micro-cracks was intensely observed in the shear span. To classify AE sources into tensile and shear cracks, AE parameter analysis was also applied. As a result, most of AE hits are classified into tensile cracks. The difference between results obtained by the AE parameter analysis and by the SiGMA analysis is investigated and discussed.

Visible wavelength surface-enhanced Raman spectroscopy from In-InP nanopillars for biomolecule detection

NASA Astrophysics Data System (ADS)

Murdoch, B. J.; Portoles, J. F.; Tardio, S.; Barlow, A. J.; Fletcher, I. W.; Cumpson, P. J.

2016-12-01

Visible wavelength surface-enhanced Raman spectroscopy (SERS) has been observed from bovine serum albumin (BSA) using In-InP nanopillars synthesised by Ar gas cluster ion beam sputtering of InP wafers. InP provides a high local refractive index for plasmonic In structures, which increases the wavelength of the In surface plasmon resonance. The Raman scattering signal was determined to be up to 285 times higher for BSA deposited onto In-InP nanopillars when compared with Si wafer substrates. These substrates demonstrate the label-free detection of biomolecules by visible wavelength SERS, without the use of noble metal particles.

High rate deposition system for metal-cluster/SiO x C y H z -polymer nanocomposite thin films

NASA Astrophysics Data System (ADS)

Peter, T.; Rehders, S.; Schürmann, U.; Strunskus, T.; Zaporojtchenko, V.; Faupel, F.

2013-06-01

A system for deposition of nanocomposite materials consisting of a SiO x C y H z -polymer matrix and Ag nanoclusters is presented. Ag nanoclusters with sizes between 2 and 20 nm are produced in a gas aggregation cluster source and are deposited through a focused beam at a high rate. This cluster source is presented in detail and the characteristics of the produced nanoclusters are shown. Simultaneously, a SiO x C y H z -polymer matrix is grown from the precursor hexamethyldisiloxane in an RF plasma. The beam of clusters is deposited into the growing polymer, forming the composite material. This process allows the rapid deposition of composite material with varying metal nanocluster concentrations and properties. Since the cluster generation is separated from the matrix growth, the properties of both can be controlled independently. In this study, we present two types of nanocomposite samples, in the first the Ag nanoclusters are homogeneously distributed in the matrix, in the second type the Ag nanoclusters form a layer which is covered by the matrix. These samples are investigated using transmission electron micrography to determine the morphology. Furthermore, the optical properties are probed using optical transmission spectroscopy and the plasmonic resonance behavior is discussed.

The formation of magnetic silicide Fe3Si clusters during ion implantation

NASA Astrophysics Data System (ADS)

Balakirev, N.; Zhikharev, V.; Gumarov, G.

2014-05-01

A simple two-dimensional model of the formation of magnetic silicide Fe3Si clusters during high-dose Fe ion implantation into silicon has been proposed and the cluster growth process has been computer simulated. The model takes into account the interaction between the cluster magnetization and magnetic moments of Fe atoms random walking in the implanted layer. If the clusters are formed in the presence of the external magnetic field parallel to the implanted layer, the model predicts the elongation of the growing cluster in the field direction. It has been proposed that the cluster elongation results in the uniaxial magnetic anisotropy in the plane of the implanted layer, which is observed in iron silicide films ion-beam synthesized in the external magnetic field.

Analysis of radiation-induced small Cu particle cluster formation in aqueous CuCl2

USGS Publications Warehouse

Jayanetti, Sumedha; Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

2001-01-01

Radition-induced small Cu particle cluster formation in aqueous CuCl2 was analyzed. It was noticed that nearest neighbor distance increased with the increase in the time of irradiation. This showed that the clusters approached the lattice dimension of bulk copper. As the average cluster size approached its bulk dimensions, an increase in the nearest neighbor coordination number was found with the decrease in the surface to volume ratio. Radiolysis of water by incident x-ray beam led to the reduction of copper ions in the solution to themetallic state.

Case Study of Ion Beams Observed By Cluster At Perigee

NASA Astrophysics Data System (ADS)

Sergeev, V.; Sauvaud, J.-A.; Perigee Beam Team

During substorms the short beams of ions in the keV-to-tens keV energy range are injected into the auroral flux tubes from the magnetotail (sometimes extending up to >100 keV energy) carrying the information on the source distance, scale-size and temporal history of plasma acceleration. We present observations with the CLUSTER crossing inward the auroral zone flux tubes at ~4Re distance near its perigee during the substorm activity on February 14, 2001. The ion beams cover the same region (poleward half) of the auroral oval where the low-energy ions are extracted from the ionosphere, and where the small-scale transient transverse Alfven waves are observed which carry predominantly the downward parallel Poynting flux into the ionosphere. The multiple beams were basically confirmed to be the transient effects, although some effects including the (spatial) velocity filter and the parallel electric fields (im- posed by quasineutrality requirement) may complicate the interpretation. The gener- ation region of ion beams is not limited to most poleward, newly-reconnected flux tubes; the beam generation region could extend across magnetic field inward by as much as >100km (if mapped to the ionosphere). Surprising variety of injection dis- tances observed nearly simultaneously (ranging between >60 Re and ~10 Re) have been inferred when using the full available energy and time resolution, with shorter injection distances be possibly associated with the flow braking process. The beam multiplicity often displays the apparent ~3 min quasiperiodicity inherent to the basic dissipation process, it was not yet explained by any substorm theory.

Symplectic multi-particle tracking on GPUs

NASA Astrophysics Data System (ADS)

Liu, Zhicong; Qiang, Ji

2018-05-01

A symplectic multi-particle tracking model is implemented on the Graphic Processing Units (GPUs) using the Compute Unified Device Architecture (CUDA) language. The symplectic tracking model can preserve phase space structure and reduce non-physical effects in long term simulation, which is important for beam property evaluation in particle accelerators. Though this model is computationally expensive, it is very suitable for parallelization and can be accelerated significantly by using GPUs. In this paper, we optimized the implementation of the symplectic tracking model on both single GPU and multiple GPUs. Using a single GPU processor, the code achieves a factor of 2-10 speedup for a range of problem sizes compared with the time on a single state-of-the-art Central Processing Unit (CPU) node with similar power consumption and semiconductor technology. It also shows good scalability on a multi-GPU cluster at Oak Ridge Leadership Computing Facility. In an application to beam dynamics simulation, the GPU implementation helps save more than a factor of two total computing time in comparison to the CPU implementation.

Spectral structure of a polycapillary lens shaped X-ray beam

NASA Astrophysics Data System (ADS)

Gogolev, A. S.; Filatov, N. A.; Uglov, S. R.; Hampai, D.; Dabagov, S. B.

2018-04-01

Polycapillary X-ray optics is widely used in X-ray analysis techniques to create a small secondary source, for instance, or to deliver X-rays to the point of interest with minimum intensity losses [1]. The main characteristics of the analytical devices on its base are the size and divergence of the focused or translated beam. In this work, we used the photon-counting pixel detector ModuPIX to study the parameters for polycapillary focused X-ray tube radiation as well as the energy and spatial dependences of radiation at the focus. We have characterized the high-speed spectral camera ModuPIX, which is a single Timepix device with a fast parallel readout allowing up to 850 frames per second with 256 × 256 pixels and a 55 μm pitch defined by the frame frequency. By means of the silicon monochromator the energy response function is measured in clustering mode by the energy scan over total X-ray tube spectrum.

Damage detection methodology under variable load conditions based on strain field pattern recognition using FBGs, nonlinear principal component analysis, and clustering techniques

NASA Astrophysics Data System (ADS)

Sierra-Pérez, Julián; Torres-Arredondo, M.-A.; Alvarez-Montoya, Joham

2018-01-01

Structural health monitoring consists of using sensors integrated within structures together with algorithms to perform load monitoring, damage detection, damage location, damage size and severity, and prognosis. One possibility is to use strain sensors to infer structural integrity by comparing patterns in the strain field between the pristine and damaged conditions. In previous works, the authors have demonstrated that it is possible to detect small defects based on strain field pattern recognition by using robust machine learning techniques. They have focused on methodologies based on principal component analysis (PCA) and on the development of several unfolding and standardization techniques, which allow dealing with multiple load conditions. However, before a real implementation of this approach in engineering structures, changes in the strain field due to conditions different from damage occurrence need to be isolated. Since load conditions may vary in most engineering structures and promote significant changes in the strain field, it is necessary to implement novel techniques for uncoupling such changes from those produced by damage occurrence. A damage detection methodology based on optimal baseline selection (OBS) by means of clustering techniques is presented. The methodology includes the use of hierarchical nonlinear PCA as a nonlinear modeling technique in conjunction with Q and nonlinear-T 2 damage indices. The methodology is experimentally validated using strain measurements obtained by 32 fiber Bragg grating sensors bonded to an aluminum beam under dynamic bending loads and simultaneously submitted to variations in its pitch angle. The results demonstrated the capability of the methodology for clustering data according to 13 different load conditions (pitch angles), performing the OBS and detecting six different damages induced in a cumulative way. The proposed methodology showed a true positive rate of 100% and a false positive rate of 1.28% for a 99% of confidence.

Proceeding of the 18th Intl. Workshop on Inelastic Ion-Surface Collisions (IISC-18)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reinhold, Carlos O; Krstic, Predrag S; Meyer, Fred W

2011-01-01

The main topics of this proceedings were: (1) Energy loss of particles at surfaces; (2) Scattering of atoms, ions, molecules and clusters; (3) Charge exchange between particles and surfaces; (4) Ion induced desorption, electronic and kinetic sputtering; (5) Defect formation, surface modification and nanostructuring; (6) Electron, photon and secondary ion emission due to particle impact on surfaces; (7) Sputtering, fragmentation, cluster and ion formation in SIMS and SNMS; (8) Cluster/molecular and highly charged ion beams; and (9) Laser induced desorption.

Theoretical substantiation of biological efficacy enhancement for β-delayed particle decay {sup 9}C beam: A Monte Carlo study in combination with analysis with the local effect model approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Liheng; Yan, Yuanlin; Ma, Yuanyuan

Purpose: To improve the efficacy of heavy ion therapy, β-delayed particle decay {sup 9}C beam as a double irradiation source for cancer therapy has been proposed. The authors’ previous experiment showed that relative biological effectiveness (RBE) values at the depths around the Bragg peak of a {sup 9}C beam were enhanced and compared to its stable counterpart {sup 12}C beam. The purpose of this study was to explore the nature of the biological efficacy enhancement theoretically. Methods: A Monte Carlo simulation study was conducted in this study. First a simplified cell model was established so as to form a tumormore » tissue. Subsequently, the tumor tissue was imported into the Monte Carlo simulation software package GATE and then the tumor cells were virtually irradiated with comparable {sup 9}C and {sup 12}C beams, respectively, in the simulations. The transportation and particle deposition data of the {sup 9}C and {sup 12}C beams, derived from the GATE simulations, were analyzed with the authors’ local effect model implementation so as to deduce cell survival fractions. Results: The particles emitted from the decay process of deposited {sup 9}C particles around a cell nucleus increased the dose delivered to the nucleus and elicited clustered damages around the secondary particles’ trajectories. Therefore, compared to the {sup 12}C beam, the RBE value of the {sup 9}C beam increased at the depths around their Bragg peaks. Conclusions: Collectively, the increased local doses and clustered damages due to the decayed particles emitted from deposited {sup 9}C particles led to the RBE enhancement in contrast with the {sup 12}C beam. Thus, the enhanced RBE effect of a {sup 9}C beam for a simplified tumor model was shown theoretically in this study.« less

Spacecraft Antennas

NASA Technical Reports Server (NTRS)

Jamnejad, Vahraz; Manshadi, Farzin; Rahmat-Samii, Yahya; Cramer, Paul

1990-01-01

Some of the various categories of issues that must be considered in the selection and design of spacecraft antennas for a Personal Access Satellite System (PASS) are addressed, and parametric studies for some of the antenna concepts to help the system designer in making the most appropriate antenna choice with regards to weight, size, and complexity, etc. are provided. The question of appropriate polarization for the spacecraft as well as for the User Terminal Antenna required particular attention and was studied in some depth. Circular polarization seems to be the favored outcome of this study. Another problem that has generally been a complicating factor in designing the multiple beam reflector antennas, is the type of feeds (single vs. multiple element and overlapping vs. non-overlapping clusters) needed for generating the beams. This choice is dependent on certain system design factors, such as the required frequency reuse, acceptable interbeam isolation, antenna efficiency, number of beams scanned, and beam-forming network (BFN) complexity. This issue is partially addressed, but is not completely resolved. Indications are that it may be possible to use relatively simple non-overlapping clusters of only a few elements, unless a large frequency reuse and very stringent isolation levels are required.

Fragmentation analysis of α-induced reactions using clusterization approach

NASA Astrophysics Data System (ADS)

Kaur, Amandeep; Sharma, Manoj K.

2018-01-01

The dynamics of α-induced reactions are worked out over an incident beam energy Eα ∼ 10- 15 MeV using targets of different masses. The decay patterns of odd mass compound systems 117Sb*, 145Pm* and 191Ir* formed in α +113In, α +141Pr and α +187Re reactions are investigated in view of n-evaporation data. The methodology of collective clusterization is applied by optimizing the neck-length parameter ΔR and the DCM calculated cross-sections find nice agreement with the experimental data. The resulting compound systems with ACN = 117- 191 cover a wide range of compound nucleus mass, and hence give an opportunity to explore various aspects related to the dynamics involved. Moreover the neutron-proton asymmetry dependence is explored in terms of the Bulk constant (α) (in the liquid drop binding energy expression) and radius term Ri and its consequent influence on the fragmentation structure of these compound systems is investigated.

Temperature-Dependent Evolution of the Oxidation States of Cobalt and Platinum in Co 1–x Pt x Clusters under H 2 and CO + H 2 Atmospheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Bing; Khadra, Ghassan; Tuaillon-Combes, Juliette

2016-09-29

Co1-xPtx clusters of 2.9-nm size with a range of atomically precise Pt/Co atomic ratios (x = 0, 0.25, 0.5, 0.75, 1) were synthesized using the mass-selected low-energy cluster beam deposition (LECBD) technique and soft-landed onto an amorphous alumina thin film prepared by atomic layer deposition (ALD). Utilizing ex situ X-ray photoemission spectroscopy (XPS), the oxidation state of the as-made clusters supported on Al2O3 was determined after both a 1-h-long exposure to air and aging for several weeks while exposed to air. Next, the aged duster samples were characterized by grazing-incidence X-ray absorption spectroscopy (GIXAS) and then pretreated with diluted hydrogenmore » and further exposed to the mixture of diluted CO and H-2 up to 225 degrees C at atmospheric pressure, and the temperature-dependent evolutions of the particle size/shape and the oxidation states of the individual metal components within the dusters were monitored using in situ grazing-incidence small-angle X-ray scattering and X-ray absorption spectroscopy (GISAXS/GIXAS). The changes in the oxidation states of Co and Pt exhibited a nonlinear dependence on the Pt/Co atomic ratio of the dusters. For example, a low Pt/Co ratio (x <= 0.5) facilitates the formation of Co(OH)(2), whereas a high Pt/Co ratio (x = 0.75) stabilizes the Co3O4 composition instead through the formation of a Co-Pt core-shell structure where the platinum shell inhibits the reduction of cobalt in the core of the Co1-xPtx alloy dusters. The obtained results indicate methods for optimizing the composition and structure of binary alloy clusters for catalysis.« less

Resolution studies with the DATURA beam telescope

NASA Astrophysics Data System (ADS)

Jansen, H.

2016-12-01

Detailed studies of the resolution of a EUDET-type beam telescope are carried out using the DATURA beam telescope as an example. The EUDET-type beam telescopes make use of CMOS MIMOSA 26 pixel detectors for particle tracking allowing for precise characterisation of particle-sensing devices. A profound understanding of the performance of the beam telescope as a whole is obtained by a detailed characterisation of the sensors themselves. The differential intrinsic resolution as measured in a MIMOSA 26 sensor is extracted using an iterative pull method, and various quantities that depend on the size of the cluster produced by a traversing charged particle are discussed: the residual distribution, the intra-pixel residual-width distribution and the intra-pixel density distribution of track incident positions.

Ionized cluster beam deposition

NASA Technical Reports Server (NTRS)

Kirkpatrick, A. R.

1983-01-01

Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

Development of the ion source for cluster implantation

NASA Astrophysics Data System (ADS)

Kulevoy, T. V.; Seleznev, D. N.; Kozlov, A. V.; Kuibeda, R. P.; Kropachev, G. N.; Alexeyenko, O. V.; Dugin, S. N.; Oks, E. M.; Gushenets, V. I.; Hershcovitch, A.; Jonson, B.; Poole, H. J.

2014-02-01

Bernas ion source development to meet needs of 100s of electron-volt ion implanters for shallow junction production is in progress in Institute for Theoretical and Experimental Physics. The ion sources provides high intensity ion beam of boron clusters under self-cleaning operation mode. The last progress with ion source operation is presented. The mechanism of self-cleaning procedure is described.

Dynamic Reactive Ionization with Cluster Secondary Ion Mass Spectrometry

NASA Astrophysics Data System (ADS)

Tian, Hua; Wucher, Andreas; Winograd, Nicholas

2016-02-01

Gas cluster ion beams (GCIB) have been tuned to enhance secondary ion yields by doping small gas molecules such as CH4, CO2, and O2 into an Ar cluster projectile, Arn + ( n = 1000-10,000) to form a mixed cluster. The `tailored beam' has the potential to expand the application of secondary ion mass spectrometry for two- and three-dimensional molecular specific imaging. Here, we examine the possibility of further enhancing the ionization by doping HCl into the Ar cluster. Water deposited on the target surface facilitates the dissociation of HCl. This concerted effect, occurring only at the impact site of the cluster, arises since the HCl is chemically induced to ionize to H+ and Cl- , allowing improved protonation of neutral molecular species. This hypothesis is confirmed by depth profiling through a trehalose thin film exposed to D2O vapor, resulting in ~20-fold increase in protonated molecules. The results show that it is possible to dynamically maintain optimum ionization conditions during depth profiling by proper adjustment of the water vapor pressure. H-D exchange in the trehalose molecule M was monitored upon deposition of D2O on the target surface, leading to the observation of [Mn* + H]+ or [Mn* + D]+ ions, where n = 1-8 hydrogen atoms in the trehalose molecule M have been replaced by deuterium. In general, we discuss the role of surface chemistry and dynamic reactive ionization of organic molecules in increasing the secondary ion yield.

Sub-250nm room temperature optical gain from AlGaN materials with strong compositional fluctuations

NASA Astrophysics Data System (ADS)

Pecora, Emanuele; Zhang, Wei; Sun, Haiding; Nikiforov, A.; Yin, Jian; Paiella, Roberto; Moustakas, Theodore; Dal Negro, Luca

2013-03-01

Compact and portable deep-UV LEDs and laser sources are needed for a number of engineering applications including optical communications, gas sensing, biochemical agent detection, disinfection, biotechnology and medical diagnostics. We investigate the deep-UV optical emission and gain properties of AlxGa1-xN/AlyGa1-yN multiple quantum wells structure. These structures were grown by molecular-beam epitaxy on 6H-SiC substrates resulting in either homogeneous wells or various degrees of band-structure compositional fluctuations in the form of cluster-like features within the wells. We measured the TE-polarized amplified spontaneous emission in the sample with cluster-like features and quantified the optical absorption/gain coefficients and gain spectra by the Variable Stripe Length (VSL) technique under ultrafast optical pumping. We report blue-shift and narrowing of the emission, VSL traces, gain spectra, polarization studies, and the validity of the Schalow-Townes relation to demonstrate a maximum net modal gain of 120 cm-1 at 250 nm in the sample with strong compositional fluctuations. Moreover, we measure a very low gain threshold (15 μJ/cm2) . On the other hand, we found that samples with homogeneous quantum wells lead to absorption only. In addition, we report gain measurements in graded-index-separate-confined heterostructure (GRINSCH) designed to increase the device optical confinement factor.

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

NASA Astrophysics Data System (ADS)

Maggiolo, R.; Echim, M.; Wedlund, C. Simon; Zhang, Y.; Fontaine, D.; Lointier, G.; Trotignon, J.-G.

2012-02-01

On 1 April 2004 the GUVI imager onboard the TIMED spacecraft spots an isolated and elongated polar cap arc. About 20 min later, the Cluster satellites detect an isolated upflowing ion beam above the polar cap. Cluster observations show that the ions are accelerated upward by a quasi-stationary electric field. The field-aligned potential drop is estimated to about 700 V and the upflowing ions are accompanied by a tenuous population of isotropic protons with a temperature of about 500 eV. The magnetic footpoints of the ion outflows observed by Cluster are situated in the prolongation of the polar cap arc observed by TIMED GUVI. The upflowing ion beam and the polar cap arc may be different signatures of the same phenomenon, as suggested by a recent statistical study of polar cap ion beams using Cluster data. We use Cluster observations at high altitude as input to a quasi-stationary magnetosphere-ionosphere (MI) coupling model. Using a Knight-type current-voltage relationship and the current continuity at the topside ionosphere, the model computes the energy spectrum of precipitating electrons at the top of the ionosphere corresponding to the generator electric field observed by Cluster. The MI coupling model provides a field-aligned potential drop in agreement with Cluster observations of upflowing ions and a spatial scale of the polar cap arc consistent with the optical observations by TIMED. The computed energy spectrum of the precipitating electrons is used as input to the Trans4 ionospheric transport code. This 1-D model, based on Boltzmann's kinetic formalism, takes into account ionospheric processes such as photoionization and electron/proton precipitation, and computes the optical and UV emissions due to precipitating electrons. The emission rates provided by the Trans4 code are compared to the optical observations by TIMED. They are similar in size and intensity. Data and modelling results are consistent with the scenario of quasi-static acceleration of electrons that generate a polar cap arc as they precipitate in the ionosphere. The detailed observations of the acceleration region by Cluster and the large scale image of the polar cap arc provided by TIMED are two different features of the same phenomenon. Combined together, they bring new light on the configuration of the high-latitude magnetosphere during prolonged periods of Northward IMF. Possible implications of the modelling results for optical observations of polar cap arcs are also discussed.

A generalized analysis of hydrophobic and loop clusters within globular protein sequences

PubMed Central

Eudes, Richard; Le Tuan, Khanh; Delettré, Jean; Mornon, Jean-Paul; Callebaut, Isabelle

2007-01-01

Background Hydrophobic Cluster Analysis (HCA) is an efficient way to compare highly divergent sequences through the implicit secondary structure information directly derived from hydrophobic clusters. However, its efficiency and application are currently limited by the need of user expertise. In order to help the analysis of HCA plots, we report here the structural preferences of hydrophobic cluster species, which are frequently encountered in globular domains of proteins. These species are characterized only by their hydrophobic/non-hydrophobic dichotomy. This analysis has been extended to loop-forming clusters, using an appropriate loop alphabet. Results The structural behavior of hydrophobic cluster species, which are typical of protein globular domains, was investigated within banks of experimental structures, considered at different levels of sequence redundancy. The 294 more frequent hydrophobic cluster species were analyzed with regard to their association with the different secondary structures (frequencies of association with secondary structures and secondary structure propensities). Hydrophobic cluster species are predominantly associated with regular secondary structures, and a large part (60 %) reveals preferences for α-helices or β-strands. Moreover, the analysis of the hydrophobic cluster amino acid composition generally allows for finer prediction of the regular secondary structure associated with the considered cluster within a cluster species. We also investigated the behavior of loop forming clusters, using a "PGDNS" alphabet. These loop clusters do not overlap with hydrophobic clusters and are highly associated with coils. Finally, the structural information contained in the hydrophobic structural words, as deduced from experimental structures, was compared to the PSI-PRED predictions, revealing that β-strands and especially α-helices are generally over-predicted within the limits of typical β and α hydrophobic clusters. Conclusion The dictionary of hydrophobic clusters described here can help the HCA user to interpret and compare the HCA plots of globular protein sequences, as well as provides an original fundamental insight into the structural bricks of protein folds. Moreover, the novel loop cluster analysis brings additional information for secondary structure prediction on the whole sequence through a generalized cluster analysis (GCA), and not only on regular secondary structures. Such information lays the foundations for developing a new and original tool for secondary structure prediction. PMID:17210072

Two-step entanglement concentration for arbitrary electronic cluster state

NASA Astrophysics Data System (ADS)

Zhao, Sheng-Yang; Liu, Jiong; Zhou, Lan; Sheng, Yu-Bo

2013-12-01

We present an efficient protocol for concentrating an arbitrary four-electron less-entangled cluster state into a maximally entangled cluster state. As a two-step entanglement concentration protocol (ECP), it only needs one pair of less-entangled cluster state, which makes this ECP more economical. With the help of electronic polarization beam splitter (PBS) and the charge detection, the whole concentration process is essentially the quantum nondemolition (QND) measurement. Therefore, the concentrated maximally entangled state can be remained for further application. Moreover, the discarded terms in some traditional ECPs can be reused to obtain a high success probability. It is feasible and useful in current one-way quantum computation.

Observation of novel photochemistry in the multiphoton ionization of Mo(CO) sub 6 van der Waals clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peifer, W.R.; Garvey, J.F.

1989-07-27

van der Waals clusters of Mo(CO){sub 6} generated in the free-jet expansion of a pulsed beam of seeded helium are subjected to multiphoton ionization and the product ions analyzed by quadrupole mass spectrometry. Oxomolybdenum and dioxomolybdenum ions are observed to be produced with high efficiency. This behavior is in striking contrast to that of metal carbonyl monomers and covalently bound cluster carbonyls, which under complete ligand loss prior to ionization. The observed photochemistry is ascribed to reactions between a photoproduced molybdenum atom and the ligands of neighboring Mo(CO){sub 6} solvent molecules within the van der Waals cluster.

Ionized-Cluster Beam/Partially Ionized Beam Deposition of Electro- Optical and Nonlinear Optical Organic Materials and Device Development

DTIC Science & Technology

1993-08-29

4’- CH3 O--\\\\4 4N -2 nitrostilbene NO 2J (MMONS) 4’-dimethylamfino OCH3 -N-4-stylbazolium j, o3 - 200 3125 1000 tosylate (DAST)or 0 3 (CH3)2N CH3 Styrylpyridinium PH cyanine dye 400 1490 470 ( SPCD ) SO4 (CH3 ½2N lh3 20

Fast large-scale clustering of protein structures using Gauss integrals.

PubMed

Harder, Tim; Borg, Mikael; Boomsma, Wouter; Røgen, Peter; Hamelryck, Thomas

2012-02-15

Clustering protein structures is an important task in structural bioinformatics. De novo structure prediction, for example, often involves a clustering step for finding the best prediction. Other applications include assigning proteins to fold families and analyzing molecular dynamics trajectories. We present Pleiades, a novel approach to clustering protein structures with a rigorous mathematical underpinning. The method approximates clustering based on the root mean square deviation by first mapping structures to Gauss integral vectors--which were introduced by Røgen and co-workers--and subsequently performing K-means clustering. Compared to current methods, Pleiades dramatically improves on the time needed to perform clustering, and can cluster a significantly larger number of structures, while providing state-of-the-art results. The number of low energy structures generated in a typical folding study, which is in the order of 50,000 structures, can be clustered within seconds to minutes.

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (Cmore » 2H 2) n +, just like ionized acetylene clusters. The fragmentation products result from reactive ion- molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4H 4 + and C 6H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts ( > 2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2H 2) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6H 6 + isomers. Lastly, these results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.« less

Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

PubMed Central

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; Fang, Yigang; Kostko, Oleg

2017-01-01

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion–molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C2H2)n+, just like ionized acetylene clusters. The fragmentation products result from reactive ion–molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C4H4+ and C6H6+ structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C2H2)n+ isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C6H6+ isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM. PMID:28484019

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

PubMed

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P; Fang, Yigang; Kostko, Oleg; Ahmed, Musahid; Head-Gordon, Martin

2017-05-23

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (C 2 H 2 ) n + , just like ionized acetylene clusters. The fragmentation products result from reactive ion-molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4 H 4 + and C 6 H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts (>2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2 H 2 ) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6 H 6 + isomers. These results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.

Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation

DOE PAGES

Stein, Tamar; Bandyopadhyay, Biswajit; Troy, Tyler P.; ...

2017-05-08

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations. The products change from reactive fragmentation products in a higher temperature, higher density gas regime toward a very cold collision-free cluster regime that is dominated by products whose empirical formula is (Cmore » 2H 2) n +, just like ionized acetylene clusters. The fragmentation products result from reactive ion- molecule collisions in a comparatively higher pressure and temperature regime followed by unimolecular decomposition. The isolated ionized clusters display rich dynamics that contain bonded C 4H 4 + and C 6H 6 + structures solvated with one or more neutral acetylene molecules. Such species contain large amounts ( > 2 eV) of excess internal energy. The role of the solvent acetylene molecules is to affect the barrier crossing dynamics in the potential energy surface (PES) between (C 2H 2) n + isomers and provide evaporative cooling to dissipate the excess internal energy and stabilize products including the aromatic ring of the benzene cation. Formation of the benzene cation is demonstrated in AIMD simulations of acetylene clusters with n > 3, as well as other metastable C 6H 6 + isomers. Lastly, these results suggest a path for aromatic ring formation in cold acetylene-rich environments such as parts of the ISM.« less

The study of the structural stability of the spiral laser beams propagation through inhomogeneous phase medium

NASA Astrophysics Data System (ADS)

Zinchik, Alexander A.; Muzychenko, Yana B.

2015-06-01

This paper discusses theoretical and experimental results of the investigation of light beams that retain their intensity structure during propagation and focusing. Spiral laser beams are a family of laser beams that preserve the structural stability up to scale and rotation with the propagation. Properties of spiral beams are of practical interest for laser technology, medicine and biotechnology. Researchers use a spiral beams for movement and manipulation of microparticles. Functionality laser manipulators can be significantly enhanced by using spiral beams whose intensity remains invariable. It is well known, that these beams has non-zero orbital angular momentum. Spiral beams have a complicated phase distribution in cross section. In this paper we investigate the structural stability of the laser beams having a spiral phase structure by passing them through an inhomogeneous phase medium. Laser beam is passed through a medium is characterized by a random distribution of phase in the range 0..2π. The modeling was performed using VirtualLab 5.0 (manufacturer LightTrans GmbH). Compared the intensity distribution of the spiral and ordinary laser beam after the passage of the inhomogeneous medium. It is shown that the spiral beams exhibit a significantly better structural stability during the passage phase heterogeneous environments than conventional laser beams. The results obtained in the simulation are tested experimentally. Experimental results show good agreement with the theoretical results.

Problems with small area surveys: lensing covariance of supernova distance measurements.

PubMed

Cooray, Asantha; Huterer, Dragan; Holz, Daniel E

2006-01-20

While luminosity distances from type Ia supernovae (SNe) are a powerful probe of cosmology, the accuracy with which these distances can be measured is limited by cosmic magnification due to gravitational lensing by the intervening large-scale structure. Spatial clustering of foreground mass leads to correlated errors in SNe distances. By including the full covariance matrix of SNe, we show that future wide-field surveys will remain largely unaffected by lensing correlations. However, "pencil beam" surveys, and those with narrow (but possibly long) fields of view, can be strongly affected. For a survey with 30 arcmin mean separation between SNe, lensing covariance leads to a approximately 45% increase in the expected errors in dark energy parameters.

Spring-like electroactive actuators based on paper/ionogel/metal nanocomposites

NASA Astrophysics Data System (ADS)

Santaniello, Tommaso; Migliorini, Lorenzo; Borghi, Francesca; Yan, Yunsong; Rondinini, Sandra; Lenardi, Cristina; Milani, Paolo

2018-06-01

We report about a novel class of electroactive nanocomposites designed to perform spring-like actuation at low applied voltages. These systems are based on the impregnation of plain paper with a highly conductive ionogel, interpenetrating nanostructured conducting electrodes are printed on the paper/ionogel substrate by supersonic cluster beam deposition. Due to the structure and mechanical properties of the paper substrates, helix-shaped actuators can be obtained by coiling strips of the nanocomposites, thus enabling the production of electroactive components exhibiting motion up to two millimeters with a polarization of 5 V. Our approach constitutes a promising solution for the development of adaptive soft robotic architectures and smart flexible systems with bio-inspired motility.

Cluster structures influenced by interaction with a surface.

PubMed

Witt, Christopher; Dieterich, Johannes M; Hartke, Bernd

2018-05-30

Clusters on surfaces are vitally important for nanotechnological applications. Clearly, cluster-surface interactions heavily influence the preferred cluster structures, compared to clusters in vacuum. Nevertheless, systematic explorations and an in-depth understanding of these interactions and how they determine the cluster structures are still lacking. Here we present an extension of our well-established non-deterministic global optimization package OGOLEM from isolated clusters to clusters on surfaces. Applying this approach to intentionally simple Lennard-Jones test systems, we produce a first systematic exploration that relates changes in cluster-surface interactions to resulting changes in adsorbed cluster structures.

Improved mass resolution and mass accuracy in TOF-SIMS spectra and images using argon gas cluster ion beams.

PubMed

Shon, Hyun Kyong; Yoon, Sohee; Moon, Jeong Hee; Lee, Tae Geol

2016-06-09

The popularity of argon gas cluster ion beams (Ar-GCIB) as primary ion beams in time-of-flight secondary ion mass spectrometry (TOF-SIMS) has increased because the molecular ions of large organic- and biomolecules can be detected with less damage to the sample surfaces. However, Ar-GCIB is limited by poor mass resolution as well as poor mass accuracy. The inferior quality of the mass resolution in a TOF-SIMS spectrum obtained by using Ar-GCIB compared to the one obtained by a bismuth liquid metal cluster ion beam and others makes it difficult to identify unknown peaks because of the mass interference from the neighboring peaks. However, in this study, the authors demonstrate improved mass resolution in TOF-SIMS using Ar-GCIB through the delayed extraction of secondary ions, a method typically used in TOF mass spectrometry to increase mass resolution. As for poor mass accuracy, although mass calibration using internal peaks with low mass such as hydrogen and carbon is a common approach in TOF-SIMS, it is unsuited to the present study because of the disappearance of the low-mass peaks in the delayed extraction mode. To resolve this issue, external mass calibration, another regularly used method in TOF-MS, was adapted to enhance mass accuracy in the spectrum and image generated by TOF-SIMS using Ar-GCIB in the delayed extraction mode. By producing spectra analyses of a peptide mixture and bovine serum albumin protein digested with trypsin, along with image analyses of rat brain samples, the authors demonstrate for the first time the enhancement of mass resolution and mass accuracy for the purpose of analyzing large biomolecules in TOF-SIMS using Ar-GCIB through the use of delayed extraction and external mass calibration.

Cluster signal-to-noise analysis for evaluation of the information content in an image.

PubMed

Weerawanich, Warangkana; Shimizu, Mayumi; Takeshita, Yohei; Okamura, Kazutoshi; Yoshida, Shoko; Yoshiura, Kazunori

2018-01-01

(1) To develop an observer-free method of analysing image quality related to the observer performance in the detection task and (2) to analyse observer behaviour patterns in the detection of small mass changes in cone-beam CT images. 13 observers detected holes in a Teflon phantom in cone-beam CT images. Using the same images, we developed a new method, cluster signal-to-noise analysis, to detect the holes by applying various cut-off values using ImageJ and reconstructing cluster signal-to-noise curves. We then evaluated the correlation between cluster signal-to-noise analysis and the observer performance test. We measured the background noise in each image to evaluate the relationship with false positive rates (FPRs) of the observers. Correlations between mean FPRs and intra- and interobserver variations were also evaluated. Moreover, we calculated true positive rates (TPRs) and accuracies from background noise and evaluated their correlations with TPRs from observers. Cluster signal-to-noise curves were derived in cluster signal-to-noise analysis. They yield the detection of signals (true holes) related to noise (false holes). This method correlated highly with the observer performance test (R 2 = 0.9296). In noisy images, increasing background noise resulted in higher FPRs and larger intra- and interobserver variations. TPRs and accuracies calculated from background noise had high correlation with actual TPRs from observers; R 2 was 0.9244 and 0.9338, respectively. Cluster signal-to-noise analysis can simulate the detection performance of observers and thus replace the observer performance test in the evaluation of image quality. Erroneous decision-making increased with increasing background noise.

Experimental and theoretical study on Raman spectra of magnesium fluoride clusters and solids.

PubMed

Neelamraju, S; Bach, A; Schön, J C; Fischer, D; Jansen, M

2012-11-21

In this study, the Raman and IR spectra of a large number of isomers of MgF(2) clusters and of possible bulk polymorphs of MgF(2) are calculated and compared with experimental data observed using a low-temperature atom beam deposition. The bulk polymorphs were taken from earlier work, while the cluster modifications for the neutral (MgF(2))(n) (n = 1-10) clusters and charged clusters (up to the trimer anion and cation, (Mg(3)F(7))(-) and (Mg(3)F(5))(+), respectively) are determined in the present work by global energy landscape explorations using simulated annealing. These theoretical calculations are complemented by an experimental study on both the vapor phase and the deposited films of MgF(2), which are generated in a low-temperature atom beam deposition setup for the synthesis of MgF(2) bulk phases. The MgF(2) vapor and film are characterized via Raman spectroscopy of the MgF(2) gas phase species embedded in an Ar-matrix and of the MgF(2)-films deposited onto a cooled substrate, respectively. We find that, in the vapor phase, there are monomers and dimers and charged species to be present in our experimental setup. Furthermore, the results suggest that in the amorphous bulk MgF(2), rutile-like domains are present and MgF(2) clusters similar to those in the matrix. Finally, peaks at about 800 cm(-1), which are in the same range as the A(g) modes of clusters with dangling fluorine atoms connected to three-coordinated Mg atoms, indicate that such dangling bonds are also present in amorphous MgF(2).

Spectral properties of Langmuir and beam-mode waves observed inside terrestrial foreshock by Cluster spacecraf

NASA Astrophysics Data System (ADS)

Pisa, D.; Soucek, J.; Santolik, O.

2016-12-01

Electrostatic plasma waves are commonly observed in the upstream regions of planetary shocks. Solar wind electrons accelerated at the shock front are reflected back into the solar wind and form electron beams. The electron distribution becomes unstable and electrostatic waves are generated inside the foreshock region. The processes of generation and evolution of electrostatic waves significantly depend on the solar wind plasma conditions and generally exhibit complex behavior. Langmuir waves can be identified as intense narrowband emission at the local plasma frequency and weaker broadband beam-mode waves below and above the plasma frequency deeper in the downstream region. We present a long-term survey of Langmuir and beam-mode waves in the vicinity of the plasma frequency observed upstream of the terrestrial bow shock by the Cluster spacecraft. Using solar wind data and bow shock positions from OMNI, as well as in-situ measurements of interplanetary magnetic field, we have mapped all available spacecraft positions into foreshock coordinates. For a study of plasma waves, we have used spectra and local plasma frequencies obtained from a passive and active mode of the WHISPER instrument. We show a spatial distribution of wave frequencies and spectral widths as a function of foreshock positions and solar wind conditions.

Structure based alignment and clustering of proteins (STRALCP)

DOEpatents

Zemla, Adam T.; Zhou, Carol E.; Smith, Jason R.; Lam, Marisa W.

2013-06-18

Disclosed are computational methods of clustering a set of protein structures based on local and pair-wise global similarity values. Pair-wise local and global similarity values are generated based on pair-wise structural alignments for each protein in the set of protein structures. Initially, the protein structures are clustered based on pair-wise local similarity values. The protein structures are then clustered based on pair-wise global similarity values. For each given cluster both a representative structure and spans of conserved residues are identified. The representative protein structure is used to assign newly-solved protein structures to a group. The spans are used to characterize conservation and assign a "structural footprint" to the cluster.

Numerical simulation of electron beam welding with beam oscillations

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Permyakov, G. L.

2017-02-01

This research examines the process of electron-beam welding in a keyhole mode with the use of beam oscillations. We study the impact of various beam oscillations and their parameters on the shape of the keyhole, the flow of heat and mass transfer processes and weld parameters to develop methodological recommendations. A numerical three-dimensional mathematical model of electron beam welding is presented. The model was developed on the basis of a heat conduction equation and a Navier-Stokes equation taking into account phase transitions at the interface of a solid and liquid phase and thermocapillary convection (Marangoni effect). The shape of the keyhole is determined based on experimental data on the parameters of the secondary signal by using the method of a synchronous accumulation. Calculations of thermal and hydrodynamic processes were carried out based on a computer cluster, using a simulation package COMSOL Multiphysics.

Precision alignment device

DOEpatents

Jones, N.E.

1988-03-10

Apparatus for providing automatic alignment of beam devices having an associated structure for directing, collimating, focusing, reflecting, or otherwise modifying the main beam. A reference laser is attached to the structure enclosing the main beam producing apparatus and produces a reference beam substantially parallel to the main beam. Detector modules containing optical switching devices and optical detectors are positioned in the path of the reference beam and are effective to produce an electrical output indicative of the alignment of the main beam. This electrical output drives servomotor operated adjustment screws to adjust the position of elements of the structure associated with the main beam to maintain alignment of the main beam. 5 figs.

Precision alignment device

DOEpatents

Jones, Nelson E.

1990-01-01

Apparatus for providing automatic alignment of beam devices having an associated structure for directing, collimating, focusing, reflecting, or otherwise modifying the main beam. A reference laser is attached to the structure enclosing the main beam producing apparatus and produces a reference beam substantially parallel to the main beam. Detector modules containing optical switching devices and optical detectors are positioned in the path of the reference beam and are effective to produce an electrical output indicative of the alignment of the main beam. This electrical output drives servomotor operated adjustment screws to adjust the position of elements of the structure associated with the main beam to maintain alignment of the main beam.

Ultraviolet and infrared laser-induced fragmentation of free (CF{sub 3}I){sub n} clusters in a molecular beam and (CF{sub 3}I){sub n} clusters inside or on the surface of large (Xe){sub m} clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apatin, V. M.; Lokhman, V. N.; Makarov, G. N., E-mail: gmakarov@isan.troitsk.ru

The fragmentation of free homogeneous (CF{sub 3}I){sub n} clusters in a molecular beam (n ≤ 45 is the average number of molecules in the cluster) and (CF{sub 3}I){sub n} clusters inside or on the surface of large (Xe){sub m} clusters (m ≥ 100 is the average number of atoms in the cluster) by ultraviolet and infrared laser radiations has been studied. These three types of (CF{sub 3}I){sub n} clusters are shown to have different stabilities with respect to fragmentation by both ultraviolet and infrared radiations and completely different dependences of the fragmentation probability on the energy of ultraviolet and infraredmore » radiations. When exposed to ultraviolet radiation, the free (CF{sub 3}I){sub n} clusters fragment at comparatively low fluences (Φ{sub UV} ≤ 0.15 J cm{sup −2}) and the weakest energy dependence of the fragmentation probability is observed for them. A stronger energy dependence of the fragmentation probability is observed for the (CF{sub 3}I){sub n} clusters localized inside (Xe){sub m} clusters, and the strongest dependence is observed for the (CF{sub 3}I){sub n} clusters located on the surface of (Xe){sub m} clusters. When the clusters are exposed to infrared radiation, the homogeneous (CF{sub 3}I){sub n} clusters efficiently fragment at low fluences (Φ{sub IR} ≤ 25 mJ cm{sup −2}), higher fluences (Φ{sub IR} ≈ 75 mJ cm{sup −2}) are needed for the fragmentation of the (CF{sub 3}I){sub n} localized inside (Xe){sub m} clusters, and even higher fluences (Φ{sub IR} ≈ 150 mJ cm{sup −2}) are needed for the fragmentation of the (CF{sub 3}I){sub n} clusters located on the surface of (Xe){sub m} clusters. It has been established that small (CF{sub 3}I){sub n} clusters located on the surface of (Xe){sub m} clusters do not fragment up to fluences Φ{sub IR} ≈ 250 mJ cm{sup −2}. The fragmentation efficiency of (CF{sub 3}I){sub n} clusters is shown to be the same (at the same fluence) when they are excited by both pulsed (τ{sub p} ≈ 150 ns) and continuous-wave infrared laser radiations. Possible causes of such a pattern of ultraviolet and infrared laser-induced fragmentation of these clusters are discussed.« less

Machine-learned cluster identification in high-dimensional data.

PubMed

Ultsch, Alfred; Lötsch, Jörn

2017-02-01

High-dimensional biomedical data are frequently clustered to identify subgroup structures pointing at distinct disease subtypes. It is crucial that the used cluster algorithm works correctly. However, by imposing a predefined shape on the clusters, classical algorithms occasionally suggest a cluster structure in homogenously distributed data or assign data points to incorrect clusters. We analyzed whether this can be avoided by using emergent self-organizing feature maps (ESOM). Data sets with different degrees of complexity were submitted to ESOM analysis with large numbers of neurons, using an interactive R-based bioinformatics tool. On top of the trained ESOM the distance structure in the high dimensional feature space was visualized in the form of a so-called U-matrix. Clustering results were compared with those provided by classical common cluster algorithms including single linkage, Ward and k-means. Ward clustering imposed cluster structures on cluster-less "golf ball", "cuboid" and "S-shaped" data sets that contained no structure at all (random data). Ward clustering also imposed structures on permuted real world data sets. By contrast, the ESOM/U-matrix approach correctly found that these data contain no cluster structure. However, ESOM/U-matrix was correct in identifying clusters in biomedical data truly containing subgroups. It was always correct in cluster structure identification in further canonical artificial data. Using intentionally simple data sets, it is shown that popular clustering algorithms typically used for biomedical data sets may fail to cluster data correctly, suggesting that they are also likely to perform erroneously on high dimensional biomedical data. The present analyses emphasized that generally established classical hierarchical clustering algorithms carry a considerable tendency to produce erroneous results. By contrast, unsupervised machine-learned analysis of cluster structures, applied using the ESOM/U-matrix method, is a viable, unbiased method to identify true clusters in the high-dimensional space of complex data. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Clustering of low-valence particles: structure and kinetics.

PubMed

Markova, Olga; Alberts, Jonathan; Munro, Edwin; Lenne, Pierre-François

2014-08-01

We compute the structure and kinetics of two systems of low-valence particles with three or six freely oriented bonds in two dimensions. The structure of clusters formed by trivalent particles is complex with loops and holes, while hexavalent particles self-organize into regular and compact structures. We identify the elementary structures which compose the clusters of trivalent particles. At initial stages of clustering, the clusters of trivalent particles grow with a power-law time dependence. Yet at longer times fusion and fission of clusters equilibrates and clusters form a heterogeneous phase with polydispersed sizes. These results emphasize the role of valence in the kinetics and stability of finite-size clusters.

Non-gaussian statistics of pencil beam surveys

NASA Technical Reports Server (NTRS)

Amendola, Luca

1994-01-01

We study the effect of the non-Gaussian clustering of galaxies on the statistics of pencil beam surveys. We derive the probability from the power spectrum peaks by means of Edgeworth expansion and find that the higher order moments of the galaxy distribution play a dominant role. The probability of obtaining the 128 Mpc/h periodicity found in pencil beam surveys is raised by more than one order of magnitude, up to 1%. Further data are needed to decide if non-Gaussian distribution alone is sufficient to explain the 128 Mpc/h periodicity, or if extra large-scale power is necessary.

Double-ring structure formation of intense ion beams with finite radius in a pre-formed plasma

NASA Astrophysics Data System (ADS)

Hu, Zhang-Hu; Wang, Xiao-Juan; Zhao, Yong-Tao; Wang, You-Nian

2017-12-01

The dynamic structure evolution of intense ion beams with a large edge density gradient is investigated in detail with an analytical model and two-dimensional particle-in-cell (PIC) simulations, with special attention paid to the influence of beam radius. At the initial stage of beam-plasma interactions, the ring structure is formed due to the transverse focusing magnetic field induced by the unneutralized beam current in the beam edge region. As the beam-plasma system evolves self-consistently, a second ring structure appears in the case of ion beams with a radius much larger than the plasma skin depth, due to the polarity change in the transverse magnetic field in the central regions compared with the outer, focusing field. Influences of the current-filamentation and two-stream instability on the ring structure can be clearly observed in PIC simulations by constructing two different simulation planes.

Experimental study on beam for composite CES structural system

NASA Astrophysics Data System (ADS)

Matsui, Tomoya

2017-10-01

Development study on Concrete Encase Steel (CES) composite structure system has been continuously conducted toward the practical use. CES structure is composed of steel and fiber reinforced concrete. In previous study, it was found that CES structure has good seismic performance from experimental study of columns, beam - column joints, shear walls and a two story two span frame. However, as fundamental study on CES beam could be lacking, it is necessary to understand the structural performance of CES beam. In this study, static loading tests of CES beams were conducted with experimental valuable of steel size, the presence or absence of slab and thickness of slab. And restoring characteristics, failure behavior, deformation behavior, and strength evaluation method of CES beam were investigated. As the results, it was found that CES beam showed stable hysteresis behavior. Furthermore it was found that the flexural strength of the CES beam could be evaluated by superposition strength theory.

Anti-terrorist vehicle crash impact energy absorbing barrier

DOEpatents

Swahlan, David J.

1989-01-01

An anti-terrorist vehicle crash barrier includes side support structures, crushable energy absorbing aluminum honeycomb modules, and an elongated impact-resistant beam extending between, and at its opposite ends through vertical guideways defined by, the side support structures. An actuating mechanism supports the beam at its opposite ends for movement between a lowered barrier-withdrawn position in which a traffic-supporting side of the beam is aligned with a traffic-bearing surface permitting vehicular traffic between the side support structures and over the beam, and a raised barrier-imposed position in which the beam is aligned with horizontal guideways defined in the side support structures above the traffic-bearing surface, providing an obstruction to vehicular traffic between the side support structures. The beam is movable rearwardly in the horizontal guideways with its opposite ends disposed transversely therethrough upon being impacted at its forward side by an incoming vehicle. The crushable modules are replaceably disposed in the horizontal guideways between aft ends thereof and the beam. The beam, replaceable modules, side support structures and actuating mechanism are separate and detached from one another such that the beam and replaceable modules are capable of coacting to disable and stop an incoming vehicle without causing structural damage to the side support structures and actuating mechanism.

Analysis of local bond-orientational order for liquid gallium at ambient pressure: Two types of cluster structures.

PubMed

Chen, Lin-Yuan; Tang, Ping-Han; Wu, Ten-Ming

2016-07-14

In terms of the local bond-orientational order (LBOO) parameters, a cluster approach to analyze local structures of simple liquids was developed. In this approach, a cluster is defined as a combination of neighboring seeds having at least nb local-orientational bonds and their nearest neighbors, and a cluster ensemble is a collection of clusters with a specified nb and number of seeds ns. This cluster analysis was applied to investigate the microscopic structures of liquid Ga at ambient pressure (AP). The liquid structures studied were generated through ab initio molecular dynamics simulations. By scrutinizing the static structure factors (SSFs) of cluster ensembles with different combinations of nb and ns, we found that liquid Ga at AP contained two types of cluster structures, one characterized by sixfold orientational symmetry and the other showing fourfold orientational symmetry. The SSFs of cluster structures with sixfold orientational symmetry were akin to the SSF of a hard-sphere fluid. On the contrary, the SSFs of cluster structures showing fourfold orientational symmetry behaved similarly as the anomalous SSF of liquid Ga at AP, which is well known for exhibiting a high-q shoulder. The local structures of a highly LBOO cluster whose SSF displayed a high-q shoulder were found to be more similar to the structure of β-Ga than those of other solid phases of Ga. More generally, the cluster structures showing fourfold orientational symmetry have an inclination to resemble more to β-Ga.

Cluster-impact fusion, or beam-contaminant fusion? (abstract)a),b)

NASA Astrophysics Data System (ADS)

Lo, Daniel H.; Petrasso, Richard D.; Wenzel, Kevin W.

1992-10-01

Beuhler, Friedlander, and Friedman (BFF) reported anomalously huge D-D fusion rates while bombarding deuterated targets with (D2O)N+ clusters (N˜25-1000) accelerated to ≊325 keV [R. J. Beuhler et al., Phys. Rev. Lett. 63, 1292 (1989); R. J. Beuhler et al., J. Phys. Chem. 94, 7665 (1990)] [i.e., ≊0.3 keV lab energy for D in (D2O)100+]. However, from our analysis of BFF's fusion product spectra, we conclude that their D lab energy was ˜50 keV. Therefore, no gross anomalies exist. Also, from our analysis of the BFF beam-ranging experiments through 500 μg/cm2 of Au, we conclude that light-ion-beam contaminants (e.g., D+ of order 100 keV) have not been ruled out, and are the probable cause of their fusion reactions. This work was supported by LLNL Subcontract B116798, Department of Energy (DOE) Grant No. DE-FG02-91ER54109, DOE Magnetic Fusion Energy Technology Fellowship Program (D. H. Lo), and DOE Fusion Energy Postdoctoral Research Program (Kevin W. Wenzel).

Practical 3-D Beam Pattern Based Channel Modeling for Multi-Polarized Massive MIMO Systems.

PubMed

Aghaeinezhadfirouzja, Saeid; Liu, Hui; Balador, Ali

2018-04-12

In this paper, a practical non-stationary three-dimensional (3-D) channel models for massive multiple-input multiple-output (MIMO) systems, considering beam patterns for different antenna elements, is proposed. The beam patterns using dipole antenna elements with different phase excitation toward the different direction of travels (DoTs) contributes various correlation weights for rays related towards/from the cluster, thus providing different elevation angle of arrivals (EAoAs) and elevation angle of departures (EAoDs) for each antenna element. These include the movements of the user that makes our channel to be a non-stationary model of clusters at the receiver (RX) on both the time and array axes. In addition, their impacts on 3-D massive MIMO channels are investigated via statistical properties including received spatial correlation. Additionally, the impact of elevation/azimuth angles of arrival on received spatial correlation is discussed. Furthermore, experimental validation of the proposed 3-D channel models on azimuth and elevation angles of the polarized antenna are specifically evaluated and compared through simulations. The proposed 3-D generic models are verified using relevant measurement data.

3D ToF-SIMS Analysis of Peptide Incorporation into MALDI Matrix Crystals with Sub-micrometer Resolution.

PubMed

Körsgen, Martin; Pelster, Andreas; Dreisewerd, Klaus; Arlinghaus, Heinrich F

2016-02-01

The analytical sensitivity in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is largely affected by the specific analyte-matrix interaction, in particular by the possible incorporation of the analytes into crystalline MALDI matrices. Here we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the incorporation of three peptides with different hydrophobicities, bradykinin, Substance P, and vasopressin, into two classic MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (HCCA). For depth profiling, an Ar cluster ion beam was used to gradually sputter through the matrix crystals without causing significant degradation of matrix or biomolecules. A pulsed Bi3 ion cluster beam was used to image the lateral analyte distribution in the center of the sputter crater. Using this dual beam technique, the 3D distribution of the analytes and spatial segregation effects within the matrix crystals were imaged with sub-μm resolution. The technique could in the future enable matrix-enhanced (ME)-ToF-SIMS imaging of peptides in tissue slices at ultra-high resolution. Graphical Abstract ᅟ.

Practical 3-D Beam Pattern Based Channel Modeling for Multi-Polarized Massive MIMO Systems †

PubMed Central

Aghaeinezhadfirouzja, Saeid; Liu, Hui

2018-01-01

In this paper, a practical non-stationary three-dimensional (3-D) channel models for massive multiple-input multiple-output (MIMO) systems, considering beam patterns for different antenna elements, is proposed. The beam patterns using dipole antenna elements with different phase excitation toward the different direction of travels (DoTs) contributes various correlation weights for rays related towards/from the cluster, thus providing different elevation angle of arrivals (EAoAs) and elevation angle of departures (EAoDs) for each antenna element. These include the movements of the user that makes our channel to be a non-stationary model of clusters at the receiver (RX) on both the time and array axes. In addition, their impacts on 3-D massive MIMO channels are investigated via statistical properties including received spatial correlation. Additionally, the impact of elevation/azimuth angles of arrival on received spatial correlation is discussed. Furthermore, experimental validation of the proposed 3-D channel models on azimuth and elevation angles of the polarized antenna are specifically evaluated and compared through simulations. The proposed 3-D generic models are verified using relevant measurement data. PMID:29649177

3D ToF-SIMS Analysis of Peptide Incorporation into MALDI Matrix Crystals with Sub-micrometer Resolution

NASA Astrophysics Data System (ADS)

Körsgen, Martin; Pelster, Andreas; Dreisewerd, Klaus; Arlinghaus, Heinrich F.

2016-02-01

The analytical sensitivity in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is largely affected by the specific analyte-matrix interaction, in particular by the possible incorporation of the analytes into crystalline MALDI matrices. Here we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the incorporation of three peptides with different hydrophobicities, bradykinin, Substance P, and vasopressin, into two classic MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (HCCA). For depth profiling, an Ar cluster ion beam was used to gradually sputter through the matrix crystals without causing significant degradation of matrix or biomolecules. A pulsed Bi3 ion cluster beam was used to image the lateral analyte distribution in the center of the sputter crater. Using this dual beam technique, the 3D distribution of the analytes and spatial segregation effects within the matrix crystals were imaged with sub-μm resolution. The technique could in the future enable matrix-enhanced (ME)-ToF-SIMS imaging of peptides in tissue slices at ultra-high resolution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brualla, Lorenzo, E-mail: lorenzo.brualla@uni-due.de; Zaragoza, Francisco J.; Sempau, Josep

Purpose: External beam radiotherapy is the only conservative curative approach for Stage I non-Hodgkin lymphomas of the conjunctiva. The target volume is geometrically complex because it includes the eyeball and lid conjunctiva. Furthermore, the target volume is adjacent to radiosensitive structures, including the lens, lacrimal glands, cornea, retina, and papilla. The radiotherapy planning and optimization requires accurate calculation of the dose in these anatomical structures that are much smaller than the structures traditionally considered in radiotherapy. Neither conventional treatment planning systems nor dosimetric measurements can reliably determine the dose distribution in these small irradiated volumes. Methods and Materials: The Montemore » Carlo simulations of a Varian Clinac 2100 C/D and human eye were performed using the PENELOPE and PENEASYLINAC codes. Dose distributions and dose volume histograms were calculated for the bulbar conjunctiva, cornea, lens, retina, papilla, lacrimal gland, and anterior and posterior hemispheres. Results: The simulated results allow choosing the most adequate treatment setup configuration, which is an electron beam energy of 6 MeV with additional bolus and collimation by a cerrobend block with a central cylindrical hole of 3.0 cm diameter and central cylindrical rod of 1.0 cm diameter. Conclusions: Monte Carlo simulation is a useful method to calculate the minute dose distribution in ocular tissue and to optimize the electron irradiation technique in highly critical structures. Using a voxelized eye phantom based on patient computed tomography images, the dose distribution can be estimated with a standard statistical uncertainty of less than 2.4% in 3 min using a computing cluster with 30 cores, which makes this planning technique clinically relevant.« less

Shell Evolution towards 78Ni: Low-Lying States in 77Cu

NASA Astrophysics Data System (ADS)

Sahin, E.; Bello Garrote, F. L.; Tsunoda, Y.; Otsuka, T.; de Angelis, G.; Görgen, A.; Niikura, M.; Nishimura, S.; Xu, Z. Y.; Baba, H.; Browne, F.; Delattre, M.-C.; Doornenbal, P.; Franchoo, S.; Gey, G.; Hadyńska-KlÈ©k, K.; Isobe, T.; John, P. R.; Jung, H. S.; Kojouharov, I.; Kubo, T.; Kurz, N.; Li, Z.; Lorusso, G.; Matea, I.; Matsui, K.; Mengoni, D.; Morfouace, P.; Napoli, D. R.; Naqvi, F.; Nishibata, H.; Odahara, A.; Sakurai, H.; Schaffner, H.; Söderström, P.-A.; Sohler, D.; Stefan, I. G.; Sumikama, T.; Suzuki, D.; Taniuchi, R.; Taprogge, J.; Vajta, Z.; Watanabe, H.; Werner, V.; Wu, J.; Yagi, A.; Yalcinkaya, M.; Yoshinaga, K.

2017-06-01

The level structure of the neutron-rich 77Cu nucleus is investigated through β -delayed γ -ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of 77Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in 77Cu are identified for the first time by correlating γ rays with the β decay of 77Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near 78Ni and suggests a single-particle nature for both the 5 /21- and 3 /21- states in 77Cu, leading to doubly magic 78Ni.

A sensor network based virtual beam-like structure method for fault diagnosis and monitoring of complex structures with Improved Bacterial Optimization

NASA Astrophysics Data System (ADS)

Wang, H.; Jing, X. J.

2017-02-01

This paper proposes a novel method for the fault diagnosis of complex structures based on an optimized virtual beam-like structure approach. A complex structure can be regarded as a combination of numerous virtual beam-like structures considering the vibration transmission path from vibration sources to each sensor. The structural 'virtual beam' consists of a sensor chain automatically obtained by an Improved Bacterial Optimization Algorithm (IBOA). The biologically inspired optimization method (i.e. IBOA) is proposed for solving the discrete optimization problem associated with the selection of the optimal virtual beam for fault diagnosis. This novel virtual beam-like-structure approach needs less or little prior knowledge. Neither does it require stationary response data, nor is it confined to a specific structure design. It is easy to implement within a sensor network attached to the monitored structure. The proposed fault diagnosis method has been tested on the detection of loosening screws located at varying positions in a real satellite-like model. Compared with empirical methods, the proposed virtual beam-like structure method has proved to be very effective and more reliable for fault localization.

Cable load sensing device

DOEpatents

Beus, Michael J.; McCoy, William G.

1998-01-01

Apparatus for sensing the magnitude of a load on a cable as the cable is employed to support the load includes a beam structure clamped to the cable so that a length of the cable lies along the beam structure. A spacer associated with the beam structure forces a slight curvature in a portion of the length of cable under a cable "no-load" condition so that the portion of the length of cable is spaced from the beam structure to define a cable curved portion. A strain gauge circuit including strain gauges is secured to the beam structure by welding. As the cable is employed to support a load the load causes the cable curved portion to exert a force normal to the cable through the spacer and on the beam structure to deform the beam structure as the cable curved portion attempts to straighten under the load. As this deformation takes place, the resistance of the strain gauges is set to a value proportional to the magnitude of the normal strain on the beam structure during such deformation. The magnitude of the normal strain is manipulated in a control device to generate a value equal to the magnitude or weight of the load supported by the cable.

Organic-inorganic hybrid resists for EUVL

NASA Astrophysics Data System (ADS)

Singh, Vikram; Kalyani, Vishwanath; Satyanarayana, V. S. V.; Pradeep, Chullikkattil P.; Ghosh, Subrata; Sharma, Satinder; Gonsalves, Kenneth E.

2014-03-01

Herein, we describe preliminary results on organic-inorganic hybrid photoresists, capable of showing line patterns up to 16 nm under e-beam exposure studies, prepared by incorporating polyoxometalates (POMs) clusters into organic photoresist materials. Various Mo and W based clusters such as (TBA)2[Mo6O19], (TBA)5(H)[P2V3W15O62] and (TBA)4[P2Mo18O61] (where TBA = tetrabutyl ammonium counter ion) have been incorporated into PMMA matrix by mixing POM solutions and standard PMMA polymer in anisole (MW ~ 95000, MicroChem) in 1:33 w/v ratio. E-beam exposure followed by development with MIBK solutions showed that these new organic-inorganic hybrid photoresists show good line patterns upto 16 nm, which were not observed in the case of control experiments done on pure PMMA polymer resist. The observed enhancement of resist properties in the case of hybrid resists could possibly be due to a combination of features imparted to the resist by the POM clusters such as increased sensitivity, etch resistance and thermal stability.

Gas cluster ion beam for the characterization of organic materials in submarine basalts as Mars analogs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sano, Naoko, E-mail: naoko.sano@ncl.ac.uk; Barlow, Anders J.; Cumpson, Peter J.

The solar system contains large quantities of organic compounds that can form complex molecular structures. The processing of organic compounds by biological systems leads to molecules with distinctive structural characteristics; thus, the detection and characterization of organic materials could lead to a high degree of confidence in the existence of extra-terrestrial life. Given the nature of the surface of most planetary bodies in the solar system, evidence of life is more likely to be found in the subsurface where conditions are more hospitable. Basalt is a common rock throughout the solar system and the primary rock type on Mars andmore » Earth. Basalt is therefore a rock type that subsurface life might exploit and as such a suitable material for the study of methods required to detect and analyze organic material in rock. Telluric basalts from Earth represent an analog for extra-terrestrial rocks where the indigenous organic matter could be analyzed for molecular biosignatures. This study focuses on organic matter in the basalt with the use of surface analysis techniques utilizing Ar gas cluster ion beams (GCIB); time of flight secondary ion mass spectrometry (ToF-SIMS), and x-ray photoelectron spectroscopy (XPS), to characterize organic molecules. Tetramethylammonium hydroxide (TMAH) thermochemolysis was also used to support the data obtained using the surface analysis techniques. The authors demonstrate that organic molecules were found to be heterogeneously distributed within rock textures. A positive correlation was observed to exist between the presence of microtubule textures in the basalt and the organic compounds detected. From the results herein, the authors propose that ToF-SIMS with an Ar GCIB is effective at detecting organic materials in such geological samples, and ToF-SIMS combined with XPS and TMAH thermochemolysis may be a useful approach in the study of extra-terrestrial organic material and life.« less

Microsolvation of the 5-hydroxyindole cation (5HI+) with nonpolar and quadrupolar ligands: Infrared photodissociation spectra of 5HI+-Ln clusters with L = Ar and N2 (n ≤ 3)

NASA Astrophysics Data System (ADS)

Klyne, Johanna; Dopfer, Otto

2017-07-01

Solvation of biomolecules and their building blocks has a strong influence on their structure and function. Herein we characterize the initial microsolvation of the 5-hydroxyindole cation (5HI+) in its 2A″ ground electronic state with nonpolar and quadrupolar ligands (L = Ar, N2) by infrared photodissociation (IRPD) spectroscopy of cold and mass-selected 5HI+-Ln (n ≤ 3) clusters in a molecular beam and dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ). The isomer-selective OH and NH stretch frequency shifts (ΔνOH/NH) disentangle the competition between H-bonding to the acidic OH and NH groups and π-stacking to the conjugated bicyclic aromatic π-electron system, the intermolecular interaction strengths, and the cluster growth sequence. For 5HI+-Arn, H-bonding and π-stacking strongly compete, indicating that dispersion forces are important for the interaction of 5HI+ with nonpolar ligands. In contrast, for 5HI+-(N2)n clusters, the H-bonds are much stronger than the π-bonds and largely determine the initial solvation process. In all clusters, the OH…L bonds are stronger than the NH…L bonds followed by the π-bonds. The interaction of 5HI+ with N2 is roughly twice stronger than with Ar, mainly due to the additional quadrupole moment of N2. The nature and strength of the individual interactions are quantified by the noncovalent interaction approach. Comparison of 5HI+-L with the corresponding neutral clusters reveals the strong impact of ionization on the total and relative interaction strengths of the H-bonds and π-bonds. In addition, comparison of 5HI+-L with corresponding clusters of the phenol, indole, and pyrrole radical cations illustrates the effects of substitution of functional groups and the addition of aromatic rings to the various subunits of 5HI on the intermolecular potential.

Phase transformations in Ln2O3 materials irradiated with swift heavy ions

NASA Astrophysics Data System (ADS)

Tracy, Cameron L.; Lang, Maik; Zhang, Fuxiang; Trautmann, Christina; Ewing, Rodney C.

2015-11-01

Phase transformations induced in the cubic C-type lanthanide sesquioxides, Ln2O3 (Ln = Sm, Gd, Ho, Tm, and Lu), by dense electronic excitation are investigated. The structural modifications resulting from exposure to beams of 185 MeV Xe and 2246 MeV Au ions are characterized using synchrotron x-ray diffraction and Raman spectroscopy. The formation of a B-type polymorph, an X-type nonequilibrium phase, and an amorphous phase are observed. The specific phase formed and the transformation rate show dependence on the material composition, as well as the ion beam mass and energy. Atomistic mechanisms for these transformations are determined, indicating that formation of the B-type phase results from the production of anti-Frenkel defects and the aggregation of anion vacancies into planar clusters, whereas formation of the X-type and amorphous phases requires extensive displacement of both anions and cations. The observed variations in phase behavior with changing lanthanide ionic radius and deposited electronic energy density are related to the energetics of these transformation mechanisms.

Development of a composite geodetic structure for space construction, phase 1A

NASA Technical Reports Server (NTRS)

1980-01-01

The development of a geodetic beam and beam builder for on orbit construction of large truss type space structures is discussed. The geodetic beam is a lightweight, open lattice structure composed of an equilateral gridwork of crisscrossing rods. The beam provides a high degree of stiffness and minimizes structural distortion, due to temperature gradients, through the incorporation of a new graphite and glass reinforced thermoplastic composite material with a low coefficient of thermal expansion. A low power consuming, high production rate, beam builder automatically fabricates the geodetic beams in space using rods preprocessed on Earth. Three areas of the development are focused upon; (1) geodetic beam designs for local attachment of equipment or beam to beam joining in a parallel or crossing configurations, (2) evaluation of long life pultruded rods capable of service temperatures higher than possible with the HMS/P1700 rod material, and (3) evalaution of high temperature joint encapsulant materials.

Electron cyclotron resonance plasma production by using pulse mode microwaves and dependences of ion beam current and plasma parameters on the pulse condition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiriyama, Ryutaro; Takenaka, Tomoya; Kurisu, Yousuke

2012-02-15

We measure the ion beam current and the plasma parameters by using the pulse mode microwave operation in the first stage of a tandem type ECRIS. The time averaged extracted ion beam current in the pulse mode operation is larger than that of the cw mode operation with the same averaged microwave power. The electron density n{sub e} in the pulse mode is higher and the electron temperature T{sub e} is lower than those of the cw mode operation. These plasma parameters are considered to cause in the increase of the ion beam current and are suitable to produce molecularmore » or cluster ions.« less

A neutral hydrogen survey of the Hydra 1 cluster

NASA Technical Reports Server (NTRS)

Mcmahon, Pauline; Vangorkom, Jacqueline; Richter, Otto; Ferguson, Henry

1993-01-01

We are undertaking a project to image the entire volume of the Hydra 1 cluster of galaxies in neutral hydrogen using the VLA. This involves making a series of pointings spaced 30 min. (the half power beam width) apart, each observed at three velocity settings in order to span the whole velocity range of the cluster. The purpose of this survey is to determine the true distribution, both in space and velocity, of gas-rich systems and hence, to deduce what effects a dense environment may have on the evolution of these systems. Most surveys of clusters to date have been performed on optically selected samples. However, optically selected samples may provide misleading views of the distribution of gas-rich systems, since many low surface brightness galaxies have an abundance of neutral gas (Bothun et al. 1987, Giovanelli & Haynes 1989). The Hydra project is providing the first unbiased view of the HI distribution in a cluster of galaxies. Our 5 sigma sensitivity is 4.1 x 10(exp 7) solar M/beam, (assuming H(sub 0) = 75 km s(exp -1) Mpc(exp -1)) and our velocity resolution is 42 km s(exp -1). We have a spatial resolution of 45 sec., which means that only the largest galaxies are spatially resolved enough to determine HI disk size. Our coverage is about 50 percent of the central region plus eight other fields centered on bright spirals within about 2 deg. of the center.

Invariant Clustering Using Scattering Matrices.

DTIC Science & Technology

1983-02-23

general three-dimensional elasticity a discontinuous fiber, however. equations for an anisotropic beam have been used by Sayir [19] to show that shear...34 Exptl. tives for Viscoelastic Constitutive Equations " Tech.,6(2), pp 10-14 (Apr 1982). (Submitted to J. Rheology, Apr 1982). 63. Gibson, R.F., Yau, A...vibration modes up to about nine nodes [4], Added mass of water. The frequency range relevant In the Timoshenko beam equations governing free, for ship

Relaxation times measurement in single and multiply excited xenon clusters

NASA Astrophysics Data System (ADS)

Serdobintsev, P. Yu.; Melnikov, A. S.; Pastor, A. A.; Timofeev, N. A.; Khodorkovskiy, M. A.

2018-05-01

Direct measurement of the rates of nonradiative relaxation processes in electronically excited xenon clusters was carried out. The clusters were created in a pulsed supersonic beam and two-photon excited by femtosecond laser pulses with a wavelength of 263 nm. The measurements were performed using the pump-probe method and electron spectroscopy. It is shown that relaxation of light clusters XeN (N < 15) predominantly occurs by desorption of excited xenon atoms with a characteristic time constant of 3 ps. Heavier electronically excited clusters (N > 10) vibrationally relax to the lowest electronically excited state at a rate of about 0.075 eV/ps. Multiply excited clusters are deactivated via energy exchange between excited centers with the ionization of one of them. The production of electrons in this process occurs with a delay of ˜4 ps from the pump pulse, and the process is completed in 10 ps.

A transmission electron microscopy and X-ray photoelectron spectroscopy study of annealing induced γ-phase nucleation, clustering, and interfacial dynamics in reactively sputtered amorphous alumina thin films

NASA Astrophysics Data System (ADS)

Kumar, A. K. Nanda; Prasanna, S.; Subramanian, B.; Jayakumar, S.; Rao, G. Mohan

2015-03-01

Pure α-Al2O3 exhibits a very high degree of thermodynamical stability among all metal oxides and forms an inert oxide scale in a range of structural alloys at high temperatures. We report that amorphous Al2O3 thin films sputter deposited over crystalline Si instead show a surprisingly active interface. On annealing, crystallization begins with nuclei of a phase closely resembling γ-Alumina forming almost randomly in an amorphous matrix, and with increasing frequency near the substrate/film interface. This nucleation is marked by the signature appearance of sharp (400) and (440) reflections and the formation of a diffuse diffraction halo with an outer maximal radius of ≈0.23 nm enveloping the direct beam. The microstructure then evolves by a cluster-coalescence growth mechanism suggestive of swift nucleation and sluggish diffusional kinetics, while locally the Al ions redistribute slowly from chemisorbed and tetrahedral sites to higher anion coordinated sites. Chemical state plots constructed from XPS data and simple calculations of the diffraction patterns from hypothetically distorted lattices suggest that the true origins of the diffuse diffraction halo are probably related to a complex change in the electronic structure spurred by the a-γ transformation rather than pure structural disorder. Concurrent to crystallization within the film, a substantially thick interfacial reaction zone also builds up at the film/substrate interface with the excess Al acting as a cationic source.

First measurement of the 2.4 MeV and 2.9 MeV 6He three-cluster resonant states via the 3H(4He, pα)2n four-body reaction

NASA Astrophysics Data System (ADS)

Mandaglio, Giuseppe; Povoroznyk, Orest; Gorpinich, Olga K.; Jachmenjov, Olexiy O.; Anastasi, Antonio; Curciarello, Francesca; de Leo, Veronica; Mokhnach, Hanna V.; Ponkratenko, Oleg; Roznyuk, Yuri; Fazio, Giovanni; Giardina, Giorgio

2014-06-01

Two new low-lying 6He levels at excitation energies of about 2.4 MeV and 2.9 MeV were observed in the experimental investigation of the p-α coincidence spectra obtained by the 3H(4He, pα)2n four-body reaction at E4He beam energy of 27.2 MeV. The relevant E* peak energy and Γ energy width spectroscopic parameters for such 6He* excited states decaying into the α+n+n channel were obtained by analyzing the bidimensional (Ep, Eα) energy spectra. The present new result of two low-lying 6He* excited states above the 4He+2n threshold energy of 0.974 MeV is important for the investigation of the nuclear structure of neutron-rich light nuclei and also as a basic test for theoretical models in the study of the three-cluster resonance feature of 6He.

Determination of ionization energies of CnN (n=4-12): Vacuum-ultraviolet (VUV) photoionization experiments and theoretical calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostko, Oleg; Zhou, Jia; Sun, Bian Jian

2010-06-10

Results from single photon vacuum ultraviolet photoionization of astrophysically relevant CnN clusters, n = 4 - 12, in the photon energy range of 8.0 eV to 12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the CnN species. A search through numerous nitrogen-terminated CnN isomers for n=4-9 indicates that the linear isomer has the lowest energy, and therefore should be the most abundant isomer in the molecular beam. Comparison with calculated results also shed light on the energetics of the linear CnN clusters, particularly in the trends of the even-carbonmore » and the odd-carbon series. These results can help guide the search of potential astronomical observations of these neutral molecules together with their cations in highly ionized regions or regions with a high UV/VUV photon flux (ranging from the visible to VUV with flux maxima in the Lyman- region) in the interstellar medium.« less

Determination of ionization energies of CnN (n=4-12): Vacuum-ultraviolet (VUV) photoionization experiments and theoretical calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostko, Oleg; Zhou, Jia; Sun, Bian Jian

2010-03-02

Results from single photon vacuum ultraviolet photoionization of astrophysically relevant CnN clusters, n = 4 - 12, in the photon energy range of 8.0 eV to 12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the CnN species. A search through numerous nitrogen-terminated CnN isomers for n=4-9 indicates that the linear isomer has the lowest energy, and therefore should be the most abundant isomer in the molecular beam. Comparison with calculated results also shed light on the energetics of the linear CnN clusters, particularly in the trends of the even-carbonmore » and the odd-carbon series. These results can help guide the search of potential astronomical observations of these neutral molecules together with their cations in highly ionized regions or regions with a high UV/VUV photon flux (ranging from the visible to VUV with flux maxima in the Lyman-a region) in the interstellar medium.« less

Cosmic Infrared Background Sources Clustered Around Quasars

NASA Astrophysics Data System (ADS)

Hall, Kirsten R.; Zakamska, Nadia; Marriage, Tobias; Crichton, Devin; Gralla, Megan

2017-06-01

Powerful quasars can be seen out to large distances. As they reside in massive dark matter halos, they provide a useful tracer of large scale structure. We stack Herschel-SPIRE images at 250, 350, and 500 microns at the locations of 13,000 quasars in redshift bins spanning 0.5 < z < 3.5. While the detected signal is dominated on instrumental beam scales by the unresolved dust emission of the quasar and its host galaxy, at z 2 the extended emission is clearly spatially resolved on Mpc scales. This emission is due to star-forming galaxies clustered around the dark matter halos hosting quasars. We measure radial surface brightness profiles of the stacked images to compute the angular correlation function of dusty star-forming galaxies correlated with quasars. We generate a halo occupation distribution model in order to determine the masses of the dark matter halos in which dusty star forming galaxies reside. We are probing potential changes in the halo mass most efficient at hosting star forming galaxies, and assessing any evidence that this halo mass evolved with redshift in the context of "cosmic downsizing".

Cryogenically cooled octupole ion trap for spectroscopy of biomolecular ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyarkin, Oleg V., E-mail: oleg.boiarkin@epfl.ch; Kopysov, Vladimir

2014-03-15

We present here the design of a linear octupole ion trap, suitable for collisional cryogenic cooling and spectroscopy of large ions. The performance of this trap has been assessed using ultraviolet (UV) photofragmentation spectroscopy of protonated dipeptides. At the trap temperature of 6.1 K, the vibrational temperature of the ions reaches 9.1 K, although their estimated translational temperature is ∼150 K. This observation suggests that, despite the significant translational heating by radio-frequency electrical field, vibrational cooling of heavy ions in the octupole is at least as efficient as in the 22-pole ion traps previously used in our laboratory. In contrastmore » to the 22-pole traps, excellent radial confinement of ions in the octupole makes it convenient for laser spectroscopy and boosts the dissociation yield of the stored ions to 30%. Overlap of the entire ion cloud by the laser beam in the octupole also allows for efficient UV depletion spectroscopy of ion–He clusters. The measured electronic spectra of the dipeptides and the clusters differ drastically, complicating a use of UV tagging spectroscopy for structural determination of large species.« less

Cryogenically cooled octupole ion trap for spectroscopy of biomolecular ions.

PubMed

Boyarkin, Oleg V; Kopysov, Vladimir

2014-03-01

We present here the design of a linear octupole ion trap, suitable for collisional cryogenic cooling and spectroscopy of large ions. The performance of this trap has been assessed using ultraviolet (UV) photofragmentation spectroscopy of protonated dipeptides. At the trap temperature of 6.1 K, the vibrational temperature of the ions reaches 9.1 K, although their estimated translational temperature is ~150 K. This observation suggests that, despite the significant translational heating by radio-frequency electrical field, vibrational cooling of heavy ions in the octupole is at least as efficient as in the 22-pole ion traps previously used in our laboratory. In contrast to the 22-pole traps, excellent radial confinement of ions in the octupole makes it convenient for laser spectroscopy and boosts the dissociation yield of the stored ions to 30%. Overlap of the entire ion cloud by the laser beam in the octupole also allows for efficient UV depletion spectroscopy of ion-He clusters. The measured electronic spectra of the dipeptides and the clusters differ drastically, complicating a use of UV tagging spectroscopy for structural determination of large species.

Bigelow Expandable Activity Module (BEAM) - ISS Inflatable Module Technology Demonstration

NASA Technical Reports Server (NTRS)

Dasgupta, Rajib; Munday, Steve; Valle, Gerard D.

2014-01-01

INNOVATION: BEAM is a pathway project demonstrating the design, fabrication, test, certification, integration, operation, on-orbit performance, and disposal of the first ever man-rated space inflatable structure. The groundwork laid through the BEAM project will support developing and launching a larger inflatable space structure with even greater mass per volume (M/V) advantages need for longer space missions. OVERVIEW: Inflatable structures have been shown to have much lower mass per volume ratios (M/V) when compared with conventional space structures. BEAM is an expandable structure, launched in a packed state, and then expanded once on orbit. It is a temporary experimental module to be used for gathering structural, thermal, and radiation data while on orbit. BEAM will be launched on Space X-8, be extracted from the dragon trunk, and will attach to ISS at Node 3- Aft. BEAM performance will be monitored over a two-year period and then BEAM will be jettison using the SSRMS.

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate

PubMed Central

Nivas, Jijil JJ; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-01-01

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams. PMID:28169342

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate.

PubMed

Nivas, Jijil Jj; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-02-07

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams.

Surface Structuring with Polarization-Singular Femtosecond Laser Beams Generated by a q-plate

NASA Astrophysics Data System (ADS)

Nivas, Jijil Jj; Cardano, Filippo; Song, Zhenming; Rubano, Andrea; Fittipaldi, Rosalba; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2017-02-01

In the last few years femtosecond optical vortex beams with different spatial distributions of the state of polarization (e.g. azimuthal, radial, spiral, etc.) have been used to generate complex, regular surface patterns on different materials. Here we present an experimental investigation on direct femtosecond laser surface structuring based on a larger class of vector beams generated by means of a q-plate with topological charge q = +1/2. In fact, voltage tuning of q-plate optical retardation allows generating a family of ultrashort laser beams with a continuous spatial evolution of polarization and fluence distribution in the focal plane. These beams can be thought of as a controlled coherent superposition of a Gaussian beam with uniform polarization and a vortex beam with a radial or azimuthal state of polarization. The use of this family of ultrashort laser beams in surface structuring leads to a further extension of the achievable surface patterns. The comparison of theoretical predictions of the vector beam characteristics at the focal plane and the generated surface patterns is used to rationalize the dependence of the surface structures on the local state of the laser beam, thus offering an effective way to either design unconventional surface structures or diagnose complex ultrashort laser beams.

Reliability Modeling of Double Beam Bridge Crane

NASA Astrophysics Data System (ADS)

Han, Zhu; Tong, Yifei; Luan, Jiahui; Xiangdong, Li

2018-05-01

This paper briefly described the structure of double beam bridge crane and the basic parameters of double beam bridge crane are defined. According to the structure and system division of double beam bridge crane, the reliability architecture of double beam bridge crane system is proposed, and the reliability mathematical model is constructed.

A novel complex networks clustering algorithm based on the core influence of nodes.

PubMed

Tong, Chao; Niu, Jianwei; Dai, Bin; Xie, Zhongyu

2014-01-01

In complex networks, cluster structure, identified by the heterogeneity of nodes, has become a common and important topological property. Network clustering methods are thus significant for the study of complex networks. Currently, many typical clustering algorithms have some weakness like inaccuracy and slow convergence. In this paper, we propose a clustering algorithm by calculating the core influence of nodes. The clustering process is a simulation of the process of cluster formation in sociology. The algorithm detects the nodes with core influence through their betweenness centrality, and builds the cluster's core structure by discriminant functions. Next, the algorithm gets the final cluster structure after clustering the rest of the nodes in the network by optimizing method. Experiments on different datasets show that the clustering accuracy of this algorithm is superior to the classical clustering algorithm (Fast-Newman algorithm). It clusters faster and plays a positive role in revealing the real cluster structure of complex networks precisely.

Shaping propagation invariant laser beams

NASA Astrophysics Data System (ADS)

Soskind, Michael; Soskind, Rose; Soskind, Yakov

2015-11-01

Propagation-invariant structured laser beams possess several unique properties and play an important role in various photonics applications. The majority of propagation invariant beams are produced in the form of laser modes emanating from stable laser cavities. Therefore, their spatial structure is limited by the intracavity mode formation. We show that several types of anamorphic optical systems (AOSs) can be effectively employed to shape laser beams into a variety of propagation invariant structured fields with different shapes and phase distributions. We present a propagation matrix approach for designing AOSs and defining mode-matching conditions required for preserving propagation invariance of the output shaped fields. The propagation matrix approach was selected, as it provides a more straightforward approach in designing AOSs for shaping propagation-invariant laser beams than the alternative technique based on the Gouy phase evolution, especially in the case of multielement AOSs. Several practical configurations of optical systems that are suitable for shaping input laser beams into a diverse variety of structured propagation invariant laser beams are also presented. The laser beam shaping approach was applied by modeling propagation characteristics of several input laser beam types, including Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian structured field distributions. The influence of the Ince-Gaussian beam semifocal separation parameter and the azimuthal orientation between the input laser beams and the AOSs onto the resulting shape of the propagation invariant laser beams is presented as well.

A Multiple Sphere T-Matrix Fortran Code for Use on Parallel Computer Clusters

NASA Technical Reports Server (NTRS)

Mackowski, D. W.; Mishchenko, M. I.

2011-01-01

A general-purpose Fortran-90 code for calculation of the electromagnetic scattering and absorption properties of multiple sphere clusters is described. The code can calculate the efficiency factors and scattering matrix elements of the cluster for either fixed or random orientation with respect to the incident beam and for plane wave or localized- approximation Gaussian incident fields. In addition, the code can calculate maps of the electric field both interior and exterior to the spheres.The code is written with message passing interface instructions to enable the use on distributed memory compute clusters, and for such platforms the code can make feasible the calculation of absorption, scattering, and general EM characteristics of systems containing several thousand spheres.

Transmission of cluster ions through a tandem accelerator of several stripper gases.

PubMed

Saitoh, Yuichi; Chiba, Atsuya; Narumi, Kazumasa

2009-10-01

The transmissions of carbon cluster ion beams through a tandem accelerator using several stripper gases (He, N2, CO2, and SF6) with a terminal voltage of 2.5 MV were measured as a function of the gas pressure in investigating the most suitable gas for cluster ion acceleration. This resulted in it being demonstrated that the highest transmission could be obtained using the smaller size gas, i.e., helium displayed the best performance of the four gases used. In addition, the ratio of transmissions of C(n) with helium and nitrogen increased with increases in the n, thus revealing that helium gas should prove the most effective in larger cluster ion acceleration using the same energy.

Structural attachments for large space structures

NASA Technical Reports Server (NTRS)

Pruett, E. C.; Loughead, T. E.; Robertson, K. B., III

1980-01-01

The feasibility of fabricating beams in space and using them as components of a large, crew assembled structure, was investigated. Two projects were undertaken: (1) design and development of a ground version of an automated beam builder capable of producing triangular cross section aluminum beams; and (2) design and fabrication of lap joints to connect the beams orthogonally and centroidal end caps to connect beams end to end at any desired angle. The first project produced a beam building machine which fabricates aluminum beams suitable for neutral buoyancy evaluation. The second project produced concepts for the lap joint and end cap. However, neither of these joint concepts was suitable for use by a pressure suited crew member in a zero gravity environment. It is concluded that before the beams can be evaluated the joint designs need to be completed and sufficient joints produced to allow assembly of a complex structure.

Atomic scale simulations of vapor cooled carbon clusters

NASA Astrophysics Data System (ADS)

Bogana, M. P.; Colombo, L.

2007-03-01

By means of atomistic simulations we observed the formation of many topologically non-equivalent carbon clusters formed by the condensation of liquid droplets, including: (i) standard fullerenes and onion-like structures, (ii) clusters showing extremely complex surfaces with both positive and negative curvatures and (iii) complex endohedral structures. In this work we offer a thorough structural characterization of the above systems, as well as an attempt to correlate the resulting structure to the actual protocol of growth. The IR and Raman responses of some exotic linear carbon structures have been further investigated, finding good agreement with experimental evidence of carbinoid structures in cluster-assembled films. Towards the aim of fully understanding the process of cluster-to-cluster coalescence dynamics, we further simulated an aerosol of amorphous carbon clusters at controlled temperatures. Various annealing temperatures and times have been observed, identifying different pathways for cluster ripening, ranging from simple coalescence to extensive reconstruction.

Two-dimensional mapping of polarizations of rhombohedral nanostructures in the orthorhombic phase of KNbO3 by the combined use of scanning transmission electron microscopy and convergent-beam electron diffraction

NASA Astrophysics Data System (ADS)

Tsuda, Kenji; Tanaka, Michiyoshi

2015-08-01

Rhombohedral nanostructures previously found in the orthorhombic phase of KNbO3, by convergent-beam electron diffraction [Tsuda et al., Appl. Phys. Lett. 102, 051913 (2013)], have been investigated by the combined use of scanning transmission electron microscopy and convergent-beam electron diffraction. Two-dimensional distributions of the rhombohedral nanostructures, or nanometer-scale spatial fluctuations of polarization clusters, have been successfully visualized. The correlation length of the observed spatial fluctuations of local polarizations is related to the cpc/apc ratio and the transition entropy.

Spatial structure and electronic spectrum of TiSi{/n -} clusters ( n = 6-18)

NASA Astrophysics Data System (ADS)

Borshch, N. A.; Pereslavtseva, N. S.; Kurganskii, S. I.

2014-10-01

Results from optimizing the spatial structure and calculated electronic spectra of anion clusters TiSi{/n -} ( n = 6-18) are presented. Calculations are performed within the density functional theory. Spatial structures of clusters detected experimentally are established by comparing the calculated and experimental data. It is shown that prismatic and fullerene-like structures are the ones most energetically favorable for clusters TiSi{/n -}. It is concluded that these structures are basic when building clusters with close numbers of silicon atoms.

Experimental Investigation of the Strength of Multiweb Beams with Corrugated Webs

NASA Technical Reports Server (NTRS)

Fraser, Allister F

1956-01-01

The results of an experimental investigation of the strength of multiweb beams with corrugated webs are reported. Included in the investigation were two types of connection between the web and the skin. A comparison between the structural efficiency of corrugated-web and channel-web multiweb beams is presented, and it is shown that, for a considerable range of the structural index, corrugated-web beams can be built which are structurally more efficient than channel-web beams.

Hollow structure formation of intense ion beams with sharp edge in background plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Zhang-Hu; Wang, You-Nian, E-mail: ynwang@dlut.edu.cn

The transport of intense ion beams with sharp radial beam edge in plasmas has been studied with two-dimensional electromagnetic particle simulations. The initial solid beam evolves into a hollow beam due to the nonlinear sharp transverse force peak in the regions of beam edge. The magnitude and nonlinearity of this peak are enhanced as the ion beam travels further into the plasma, due to the self-consistent interactions between the beam ions and the plasma electrons. This structure formation is shown to be independent on the beam radius.

Propagation stability of self-reconstructing Bessel beams enables contrast-enhanced imaging in thick media.

PubMed

Fahrbach, Florian O; Rohrbach, Alexander

2012-01-17

Laser beams that can self-reconstruct their initial beam profile even in the presence of massive phase perturbations are able to propagate deeper into inhomogeneous media. This ability has crucial advantages for light sheet-based microscopy in thick media, such as cell clusters, embryos, skin or brain tissue or plants, as well as scattering synthetic materials. A ring system around the central intensity maximum of a Bessel beam enables its self-reconstruction, but at the same time illuminates out-of-focus regions and deteriorates image contrast. Here we present a detection method that minimizes the negative effect of the ring system. The beam's propagation stability along one straight line enables the use of a confocal line principle, resulting in a significant increase in image contrast. The axial resolution could be improved by nearly 100% relative to the standard light-sheet techniques using scanned Gaussian beams, while demonstrating self-reconstruction also for high propagation depths.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Efficiency of passage of highly vibrationally excited CF3I molecules in a beam through a cooled converging hollow truncated cone

NASA Astrophysics Data System (ADS)

Makarov, Grigorii N.; Petin, A. N.

2006-09-01

The passage of CF3I molecules excited by high-intensity IR laser radiation to high vibrational states (with energy Ev >= 0.3-1.5 eV) and unexcited molecules in a pulsed beam through a converging truncated hollow metal cone cooled to Ts approx 80-85 K and mounted at an angle to the beam axis is studied. It is found that the excited molecules pass much more readily through the cone than the unexcited (vibrationally cold) molecules. This opens the possibility for studying the processes of energy transfer and redistribution over a cold surface covered by molecular (cluster) layers, and for separating excited and unexcited molecules in a beam.

Formation of propagation invariant laser beams with anamorphic optical systems

NASA Astrophysics Data System (ADS)

Soskind, Y. G.

2015-03-01

Propagation invariant structured laser beams play an important role in several photonics applications. A majority of propagation invariant beams are usually produced in the form of laser modes emanating from stable laser cavities. This work shows that anamorphic optical systems can be effectively employed to transform input propagation invariant laser beams and produce a variety of alternative propagation invariant structured laser beam distributions with different shapes and phase structures. This work also presents several types of anamorphic lens systems suitable for transforming the input laser modes into a variety of structured propagation invariant beams. The transformations are applied to different laser mode types, including Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian field distributions. The influence of the relative azimuthal orientation between the input laser modes and the anamorphic optical systems on the resulting transformed propagation invariant beams is presented as well.

Brome isotope selective control of CF3Br molecule clustering by IR laser radiation in gas-dynamic expansion of CF3Br - Ar mixture

NASA Astrophysics Data System (ADS)

Apatin, V. M.; Lokhman, V. N.; Makarov, G. N.; Ogurok, N.-D. D.; Ryabov, E. A.

2018-02-01

We report the results of research on the experimental control of CF3Br molecule clustering under gas-dynamic expansion of the CF3Br - Ar mixture at a nozzle exit by using IR laser radiation. A cw CO2 laser is used for exciting molecules and clusters in the beam and a time-of-flight mass-spectrometer with laser UV ionisation of particles for their detection. The parameters of the gas above the nozzle are determined (compositions and pressure) at which intensive molecule clustering occurs. It is found that in the case of the CF3Br gas without carrier when the pressure P0 above the nozzle does not exceed 4 atm, molecular clusters actually are not generated in the beam. If the gas mixture of CF3Br with argon is used at a pressure ratio 1 : N, where N >= 3, and the total pressure above the nozzle is P0 >= 2 atm, then there occurs molecule clustering. We study the dependences of the efficiency of suppressing the molecule clustering on parameters of the exciting pulse, gas parameters above the nozzle, and on a distance of the molecule irradiation zone from the nozzle exit section. It is shown that in the case of resonant vibrational excitation of gas-dynamically cooled CF3Br molecules at the nozzle exit one can realise isotope-selective suppression of molecule clustering with respect to bromine isotopes. With the CF3Br - Ar mixtures having the pressure ratio 1 : 3 and 1 : 15, the enrichment factors obtained with respect to bromine isotopes are kenr ≈ 1.05 ± 0.005 and kenr ≈ 1.06 ± 0.007, respectively, under jet irradiation by laser emission in the 9R(30) line (1084.635 cm-1). The results obtained let us assume that this method can be used to control clustering of molecules comprising heavy element isotopes, which have a small isotopic shift in IR absorption spectra.

Two-Dimensional Animal-Like Fractals in Thin Films

NASA Astrophysics Data System (ADS)

Gao, Hong-jun; Xue, Zeng-quan; Wu, Quan-de; Pang, Shi-jin

1996-02-01

We present a few unique animal-like fractal patterns in ionized-cluster-beam deposited fullerene-tetracyanoquinodimethane thin films. The fractal patterns consisting of animal-like aggregates such as "fishes" and "quasi-seahorses" have been characterized by transmission electron microscopy. The results indicate that the small aggregates of the animal-like body are composed of many single crystals whose crystalline directions are generally different. The formation of the fractal patterns can be attributed to the cluster-diffusion-limited aggregation.

Stress release structures for actuator beams with a stress gradient

NASA Astrophysics Data System (ADS)

Klaasse, G.; Puers, R.; Tilmans, H. A. C.

2007-10-01

Stress release structures are introduced in fixed-fixed beams or membranes for releasing average stress. The influence of a stress gradient on the initial deformation of a fixed-fixed beam with stress release structures is studied in this paper. The objective is to obtain actuator beams that are insensitive to both the average stress and the stress gradient. The target application for the actuator beam in this study is a surface micromachined variable capacitor with a fixed electrode at the center of the beam. An analytical one-dimensional model is derived which predicts the initial deflection of a fixed-fixed beam with one stress release structure at any location and with two stress release structures, placed symmetrically with respect to the center of the beam at any location. The initial center deflection of the beam with one stress release structure was found from the analytical modeling to be zero for a specific set of parameters, but a negative deflection is always present for this specific configuration, leading to beams that touch the substrate at undesired positions, which implies non-functional devices. The configuration with the two symmetrically placed stress release structures can have zero initial center deflection, according to the analytical model, when the stress release structures are placed at a distance of a quarter of the beam length from the anchor points. Finite-element simulations are performed for both configurations and validate the theory. Deviations from the assumed model result in small initial center deflections, but can be compensated for by a little shift of the stress release structures. Experiments are performed for less ideal configurations with two stress release structures where they are shaped as round meanders. These structures do not fully release the stress and the center deflection therefore depends on the average stress to some extent, as demonstrated by finite element simulations. However, the location can be chosen such that there is an initial center deflection that is close to zero. These experiments are, therefore, in qualitative agreement with the analytical model.

Correlated signals of cluster superfluorescence under two-and three-photon excitation of CdSe/CdS nanostructures

NASA Astrophysics Data System (ADS)

Samartsev, Vitaly; Mitrofanova, Tatiana

2017-10-01

The possibility and conditions for generation of the correlated signals of cluster superfluorescence (CSF) under two and three-quantum excitation of nanostructured samples CdSe/CdS by two crossed at the angle of 60° femtosecond beams of the Ti:Sapphire laser radiation are investigated. It is shown that intensity of the CSF signals is proportional to the cube of the number of clusters and that these collective signals are generated in mutually opposite directions k1 - k2 and k2 - k1, where k1, k2 are the wavevectors of the exciting pulses.

Possibility of Exciton Mediated Superconductivity in Nano-Sized Sn/Si Core-Shell Clusters: A Process Technology towards Heterogeneous Material in Nano-Scale

NASA Astrophysics Data System (ADS)

Kurokawa, Yuichiro; Hihara, Takehiko; Ichinose, Ikuo; Sumiyama, Kenji

2012-07-01

We have produced Sn/Si core-shell cluster assemblies by a plasma-gas-condensation cluster beam deposition apparatus. For the sample with Si content = 12 at. %, the temperature dependence of electrical resistivity exhibits a metallic behavior above 10 K and the onset of superconducting transition below 6.1 K. With decreasing temperature, the thermomagnetic curve for the sample with Si content = 8 at. % begins to decrease steadily toward negative value below 7.7 K, indicating the Meissner effect. An increase in the transition temperature, TC is attributable to exciton-type superconductivity.

Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities

PubMed Central

Ackerman, Paul J.; Qi, Zhiyuan; Lin, Yiheng; Twombly, Christopher W.; Laviada, Mauricio J.; Lansac, Yves; Smalyukh, Ivan I.

2012-01-01

Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable “optical drawing” of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators. PMID:22679553

Laser-Directed Hierarchical Assembly of Liquid Crystal Defects and Control of Optical Phase Singularities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, P. J.; Qi, Z. Y.; Lin, Y. H.

2012-06-07

Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable 'optical drawing' of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies ofmore » defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.« less

Multibeam Gpu Transient Pipeline for the Medicina BEST-2 Array

NASA Astrophysics Data System (ADS)

Magro, A.; Hickish, J.; Adami, K. Z.

2013-09-01

Radio transient discovery using next generation radio telescopes will pose several digital signal processing and data transfer challenges, requiring specialized high-performance backends. Several accelerator technologies are being considered as prototyping platforms, including Graphics Processing Units (GPUs). In this paper we present a real-time pipeline prototype capable of processing multiple beams concurrently, performing Radio Frequency Interference (RFI) rejection through thresholding, correcting for the delay in signal arrival times across the frequency band using brute-force dedispersion, event detection and clustering, and finally candidate filtering, with the capability of persisting data buffers containing interesting signals to disk. This setup was deployed at the BEST-2 SKA pathfinder in Medicina, Italy, where several benchmarks and test observations of astrophysical transients were conducted. These tests show that on the deployed hardware eight 20 MHz beams can be processed simultaneously for 640 Dispersion Measure (DM) values. Furthermore, the clustering and candidate filtering algorithms employed prove to be good candidates for online event detection techniques. The number of beams which can be processed increases proportionally to the number of servers deployed and number of GPUs, making it a viable architecture for current and future radio telescopes.

Enhanced electron yield from laser-driven wakefield acceleration in high-Z gas jets.

PubMed

Mirzaie, Mohammad; Hafz, Nasr A M; Li, Song; Liu, Feng; He, Fei; Cheng, Ya; Zhang, Jie

2015-10-01

An investigation of the electron beam yield (charge) form helium, nitrogen, and neon gas jet plasmas in a typical laser-plasma wakefield acceleration experiment is carried out. The charge measurement is made by imaging the electron beam intensity profile on a fluorescent screen into a charge coupled device which was cross-calibrated with an integrated current transformer. The dependence of electron beam charge on the laser and plasma conditions for the aforementioned gases are studied. We found that laser-driven wakefield acceleration in low Z-gas jet targets usually generates high-quality and well-collimated electron beams with modest yields at the level of 10-100 pC. On the other hand, filamentary electron beams which are observed from high-Z gases at higher densities reached much higher yields. Evidences for cluster formation were clearly observed in the nitrogen gas jet target, where we received the highest electron beam charge of ∼1.7 nC. Those intense electron beams will be beneficial for the applications on the generation of bright X-rays, gamma rays radiations, and energetic positrons via the bremsstrahlung or inverse-scattering processes.

Computational and Experimental Studies of the Radiation Response of Gd2Ti2O7 Pyrochlore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devanathan, Ram; Weber, William J.

2005-12-16

The structure and property changes in Gd2Ti2O7 (polycrystalline pyrochlore) were examined following irradiation with 1 MeV Kr+, 0.6 MeV Bi+ and 4 MeV Au2+ ions over the temperature range 30-950 K. Gd2Ti2O7 readily amorphizes with a low temperature (30 K) critical dose for amorphization of {approx} 0.15 displacements per atom (dpa). The critical temperature above which amorphization does not occur is about 1190 K. Nano-indentation studies reveal that the structural changes were accompanied by decreases of 15% in the Young's modulus. 1 MeV Kr+ irradiation of amorphous Gd2Ti2O7 at 1065 K resulted in ion-beam-assisted recrystallization. These experimental studies were complementedmore » with molecular dynamics simulations of low energy recoils in Gd2Ti2O7 and Gd2Zr2O7 using a Buckingham type potential. The displacement threshold energy surface in both pyrochlores is highly anisotropic. Displacement energies are higher for all sublattices in the titanate pyrochlore compared to the zirconate. Ti sublattice displacements require energies in excess of 100 eV, and result in multiple displacements and defect clusters. The formation of these clusters might impede dynamic defect recovery and facilitate amorphization.« less

Composition formulas of binary eutectics

PubMed Central

Ma, Y. P.; Dong, D. D.; Dong, C.; Luo, L. J.; Wang, Q.; Qiang, J. B.; Wang, Y. M.

2015-01-01

The present paper addresses the long-standing composition puzzle of eutectic points by introducing a new structural tool for the description of short-range-order structural unit, the cluster-plus-glue-atom model. In this model, any structure is dissociated into a 1st-neighbor cluster and a few glue atoms between the clusters, expressed by a cluster formula [cluster]gluex. This model is applied here to establish the structural model for eutectic liquids, assuming that a eutectic liquid consist of two subunits issued from the relevant eutectic phases, each being expressed by the cluster formula for ideal metallic glasses, i.e., [cluster](glue atom)1 or 3. A structural unit is then composed of two clusters from the relevant eutectic phases plus 2, 4, or 6 glue atoms. Such a dual cluster formulism is well validated in all boron-containing (except those located by the extreme phase diagram ends) and in some commonly-encountered binary eutectics, within accuracies below 1 at.%. The dual cluster formulas vary extensively and are rarely identical even for eutectics of close compositions. They are generally formed with two distinctly different cluster types, with special cluster matching rules such as cuboctahedron plus capped trigonal prism and rhombidodecahedron plus octahedral antiprism. PMID:26658618

Induction of apoptosis by accelerated heavy-ion beams in cultured fetal rat testes and its modification

NASA Astrophysics Data System (ADS)

Wang, Bing; Tanaka, Kaoru; Shang, Yi; Fujita, Kazuko; Ninomiya, Yasuharu; Moreno, Stephanie G.; Coffigny, Herve; Hayata, Isamu; Murakami, Masahiro; Eguchi-Kasai, Kiyomi; Nenoi, Mitsuru

The increasing human activities in space missions make the study on effects from high-LET ionizing radiation an important issue to be addressed. We reported previously that prenatal irradiations with heavy-ion beams on gestation day 15 generally induced markedly detrimental effects on prenatal gonads, postnatal testicular development and male breeding activity in rats. To explore the mechanisms involved in radiation-induced gonocyte apoptosis in fetal gonads, which played a critical role in the fate of postnatal testis development, accelerated heavy-ion irradiations and organotypic culture of Wistar fetal rat testes were applied to investigations focused on cellular and molecular events after irradiations with or without chemical addition. Results showed that, in addition to the clustered distribution, both the time course and the percentage of apoptosis in gonocytes on gestation day 15 equivalent in vitro appeared similar to that in utero after exposure to either carbon-ion beams with a LET value of about 13 keV/µm or neon-ion beams with a LET value of about 30 keV/µm. Irradiations induced increased p53 expression in a dose dependent manner and decreased expressions of p21 and Bcl- 2 by Western Blot examination. Administration of pan-caspase inhibitor prior to irradiations effectively inhibited apoptosis occurrence and reduced the extent of clustered apoptosis, while such effects were not observed with the presence of p53 inhibitor, gap junction inhibitor, or nitric oxide specific scavenger. These findings indicated that irradiations of cultured fetal rat testes manifested pathologically similar apoptosis induction in gonocytes to that in utero. P53 expression was possibly responsible for the response to radiation damage rather than induction of apoptosis. The syncytial organization of gonocytes played a key role in formation of the clustered apoptosis, an event that both gap junction inhibitor and nitric oxide specific scavenger were incapable of preventing.

Effects of manganese doping on the structure evolution of small-sized boron clusters

NASA Astrophysics Data System (ADS)

Zhao, Lingquan; Qu, Xin; Wang, Yanchao; Lv, Jian; Zhang, Lijun; Hu, Ziyu; Gu, Guangrui; Ma, Yanming

2017-07-01

Atomic doping of clusters is known as an effective approach to stabilize or modify the structures and properties of resulting doped clusters. We herein report the effect of manganese (Mn) doping on the structure evolution of small-sized boron (B) clusters. The global minimum structures of both neutral and charged Mn doped B cluster \\text{MnB}nQ (n  =  10-20 and Q  =  0, ±1) have been proposed through extensive first-principles swarm-intelligence based structure searches. It is found that Mn doping has significantly modified the grow behaviors of B clusters, leading to two novel structural transitions from planar to tubular and then to cage-like B structures in both neutral and charged species. Half-sandwich-type structures are most favorable for small \\text{MnB}n-/0/+ (n  ⩽  13) clusters and gradually transform to Mn-centered double-ring tubular structures at \\text{MnB}16-/0/+ clusters with superior thermodynamic stabilities compared with their neighbors. Most strikingly, endohedral cages become the ground-state structures for larger \\text{MnB}n-/0/+ (n  ⩾  19) clusters, among which \\text{MnB}20+ adopts a highly symmetric structure with superior thermodynamic stability and a large HOMO-LUMO gap of 4.53 eV. The unique stability of the endohedral \\text{MnB}\\text{20}+ cage is attributed to the geometric fit and formation of 18-electron closed-shell configuration. The results significantly advance our understanding about the structure and bonding of B-based clusters and strongly suggest transition-metal doping as a viable route to synthesize intriguing B-based nanomaterials.

Clustering and visualizing similarity networks of membrane proteins.

PubMed

Hu, Geng-Ming; Mai, Te-Lun; Chen, Chi-Ming

2015-08-01

We proposed a fast and unsupervised clustering method, minimum span clustering (MSC), for analyzing the sequence-structure-function relationship of biological networks, and demonstrated its validity in clustering the sequence/structure similarity networks (SSN) of 682 membrane protein (MP) chains. The MSC clustering of MPs based on their sequence information was found to be consistent with their tertiary structures and functions. For the largest seven clusters predicted by MSC, the consistency in chain function within the same cluster is found to be 100%. From analyzing the edge distribution of SSN for MPs, we found a characteristic threshold distance for the boundary between clusters, over which SSN of MPs could be properly clustered by an unsupervised sparsification of the network distance matrix. The clustering results of MPs from both MSC and the unsupervised sparsification methods are consistent with each other, and have high intracluster similarity and low intercluster similarity in sequence, structure, and function. Our study showed a strong sequence-structure-function relationship of MPs. We discussed evidence of convergent evolution of MPs and suggested applications in finding structural similarities and predicting biological functions of MP chains based on their sequence information. © 2015 Wiley Periodicals, Inc.

Study of nuclear matter in hard proton-nuclei and nuclei-nuclei collisions at the U70 accelerator (FLUKTON project proposal)

NASA Astrophysics Data System (ADS)

Antonov, N. N.; Baldin, A. A.; Viktorov, V. A.; Gapienko, V. A.; Gapienko, G. S.; Gres, V. N.; Ilyushin, M. A.; Korotkov, V. A.; Mysnik, A. I.; Prudkoglyad, A. F.; Pryanikov, D. S.; Semak, A. A.; Stavinsky, A. V.; Terekhov, V. I.; Uglekov, V. Ya.; Ukhanov, M. N.; Chuiko, B. V.; Shimansky, S. S.

2017-11-01

A two-arm spectrometer FLUKTON for investigations in the field of relativistic nuclear physics at U70 energies is proposed to be constructed on base of the existing detector SPIN (IHEP, Protvino). The main objective is to obtain new data on clusters of cold superdense nuclear matter. Interaction of a high intensity proton beam with nuclear targets and an ion beam with liquid hydrogen and nuclear targets will be studied.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wold, Isak G. B.; Barger, Amy J.; Owen, Frazer N.

We present 1.4 GHz catalogs for the cluster fields A370 and A2390 observed with the Very Large Array. These are two of the deepest radio images of cluster fields ever taken. The A370 image covers an area of 40' Multiplication-Sign 40' with a synthesized beam of {approx}1.''7 and a noise level of {approx}5.7 {mu}Jy near the field center. The A2390 image covers an area of 34' Multiplication-Sign 34' with a synthesized beam of {approx}1.''4 and a noise level of {approx}5.6 {mu}Jy near the field center. We catalog 200 redshifts for the A370 field. We construct differential number counts for themore » central regions (radius < 16') of both clusters. We find that the faint (S{sub 1.4{sub GHz}} < 3 mJy) counts of A370 are roughly consistent with the highest blank field number counts, while the faint number counts of A2390 are roughly consistent with the lowest blank field number counts. Our analyses indicate that the number counts are primarily from field radio galaxies. We suggest that the disagreement of our number counts can be largely attributed to cosmic variance.« less

Optimal design of a beam-based dynamic vibration absorber using fixed-points theory

NASA Astrophysics Data System (ADS)

Hua, Yingyu; Wong, Waion; Cheng, Li

2018-05-01

The addition of a dynamic vibration absorber (DVA) to a vibrating structure could provide an economic solution for vibration suppressions if the absorber is properly designed and located onto the structure. A common design of the DVA is a sprung mass because of its simple structure and low cost. However, the vibration suppression performance of this kind of DVA is limited by the ratio between the absorber mass and the mass of the primary structure. In this paper, a beam-based DVA (beam DVA) is proposed and optimized for minimizing the resonant vibration of a general structure. The vibration suppression performance of the proposed beam DVA depends on the mass ratio, the flexural rigidity and length of the beam. In comparison with the traditional sprung mass DVA, the proposed beam DVA shows more flexibility in vibration control design because it has more design parameters. With proper design, the beam DVA's vibration suppression capability can outperform that of the traditional DVA under the same mass constraint. The general approach is illustrated using a benchmark cantilever beam as an example. The receptance theory is introduced to model the compound system consisting of the host beam and the attached beam-based DVA. The model is validated through comparisons with the results from Abaqus as well as the Transfer Matrix method (TMM) method. Fixed-points theory is then employed to derive the analytical expressions for the optimum tuning ratio and damping ratio of the proposed beam absorber. A design guideline is then presented to choose the parameters of the beam absorber. Comparisons are finally presented between the beam absorber and the traditional DVA in terms of the vibration suppression effect. It is shown that the proposed beam absorber can outperform the traditional DVA by following this proposed guideline.

α clustering with a hollow structure: Geometrical structure of α clusters from platonic solids to fullerene shape

NASA Astrophysics Data System (ADS)

Tohsaki, Akihiro; Itagaki, Naoyuki

2018-01-01

We study α -cluster structure based on the geometric configurations with a microscopic framework, which takes full account of the Pauli principle, and which also employs an effective internucleon force including finite-range three-body terms suitable for microscopic α -cluster models. Here, special attention is focused upon the α clustering with a hollow structure; all the α clusters are put on the surface of a sphere. All the platonic solids (five regular polyhedra) and the fullerene-shaped polyhedron coming from icosahedral structure are considered. Furthermore, two configurations with dual polyhedra, hexahedron-octahedron and dodecahedron-icosahedron, are also scrutinized. When approaching each other from large distances with these symmetries, α clusters create certain local energy pockets. As a consequence, we insist on the possible existence of α clustering with a geometric shape and hollow structure, which is favored from Coulomb energy point of view. Especially, two configurations, that is, dual polyhedra of dodecahedron-icosahedron and fullerene, have a prominent hollow structure compared with the other six configurations.

New Convex and Spherical Structures of Bare Boron Clusters

NASA Astrophysics Data System (ADS)

Boustani, Ihsan

1997-10-01

New stable structures of bare boron clusters can easily be obtained and constructed with the help of an "Aufbau Principle" suggested by a systematicab initioHF-SCF and direct CI study. It is concluded that boron cluster formation can be established by elemental units of pentagonal and hexagonal pyramids. New convex and small spherical clusters different from the classical known forms of boron crystal structures are obtained by a combination of both basic units. Convex structures simulate boron surfaces which can be considered as segments of open or closed spheres. Both convex clusters B16and B46have energies close to those of their conjugate quasi-planar clusters, which are relatively stable and can be considered to act as a calibration mark. The closed spherical clusters B12, B22, B32, and B42are less stable than the corresponding conjugated quasi-planar structures. As a consequence, highly stable spherical boron clusters can systematically be predicted when their conjugate quasi-planar clusters are determined and energies are compared.

Influence of cluster-assembly parameters on the field emission properties of nanostructured carbon films

NASA Astrophysics Data System (ADS)

Ducati, C.; Barborini, E.; Piseri, P.; Milani, P.; Robertson, J.

2002-11-01

Supersonic cluster beam deposition has been used to produce films with different nanostructures by controlling the deposition parameters such as the film thickness, substrate temperature and cluster mass distribution. The field emission properties of cluster-assembled carbon films have been characterized and correlated to the evolution of the film nanostructure. Threshold fields ranging between 4 and 10 V/mum and saturation current densities as high as 0.7 mA have been measured for samples heated during deposition. A series of voltage ramps, i.e., a conditioning process, was found to initiate more stable and reproducible emission. It was found that the presence of graphitic particles (onions, nanotube embryos) in the films substantially enhances the field emission performance. Films patterned on a micrometer scale have been conditioned spot by spot by a ball-tip anode, showing that a relatively high emission site density can be achieved from the cluster-assembled material.

Experimental Electronic Spectroscopy of Two PAHs: Naphthalene and 2-METHYL Naphthalene

NASA Astrophysics Data System (ADS)

Friha, H.; Feraud, G.; Pino, T.; Brechignac, Ph.; Parneix, P.; Dhaoudi, Z.; Jaidane, N.; Galila, H.; Troy, T.; Schmidt, T.

2011-06-01

The presence of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM) was suggested in the mid-80's. Since then, their important role in the physico-chemical evolution of the ISM has been confirmed. Interstellar PAHs have been in particular proposed as possible carriers of some Diffuse Interstellar Bands (DIBs). These absorption bands are seen in the spectra of reddened stars from the visible to the near infrared and constitute a major astrophysical issue. Our purpose is to obtain electronic spectra of gas phase PAHs which will be used to probe their participation to the interstellar extinction curve from the visible (DIBs) to the UV (bump). For this goal PAHs cations represent an excellent set of target species. A new way of forming PAH+-Ar_n clusters cations has been implemented in the experimental set-up 'ICARE' at ISMO (Orsay) giving us the capability to measure the electronic spectra of cold PAH cations in the gas phase through the "Ar tagging" trick. Two molecules have been investigated in this way: naphthalene (C_1_0H_8) and 2- methyl naphthalene (C_1_1H_1_0). Clusters of naphthalene and (or 2-methyl-naphthalene) with Ar atoms are first formed in a supersonic jet, before being hit by a 281 nm laser beam which photo-ionizes the clusters which are then injected in a molecular beam through a skimmer. A tunable laser beam crossing downstream photo-dissociates the cations. The bare PAH fragments are detected using a Time-Of-Flight spectrometer while scanning the visible laser wavelength from 470 to 690 nm.

Energy dependent track structure parametrisations for protons and carbon ions based on nanometric simulations

NASA Astrophysics Data System (ADS)

Alexander, Frauke; Villagrasa, Carmen; Rabus, Hans; Wilkens, Jan J.

2015-09-01

The BioQuaRT project within the European Metrology Research Programme aims at correlating ion track structure characteristics with the biological effects of radiation and develops measurement and simulation techniques for determining ion track structure on different length scales from about 2 nm to about 10 μm. Within this framework, we investigate methods to translate track-structure quantities derived on a nanometre scale to macroscopic dimensions. Input data sets were generated by simulations of ion tracks of protons and carbon ions in liquid water using the Geant 4 Monte Carlo toolkit with the Geant4-DNA processes. Based on the energy transfer points - recorded with nanometre resolution - we investigated parametrisations of overall properties of ion track structure. Three different track structure parametrisations have been developed using the distances to the 10 next neighbouring ionisations, the radial energy distribution and ionisation cluster size distributions. These parametrisations of nanometric track structure build a basis for deriving biologically relevant mean values which are essential in the clinical situation where each voxel is exposed to a mixed radiation field. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.

Structural transition of (InSb)n clusters at n = 6-10

NASA Astrophysics Data System (ADS)

Lu, Qi Liang; Luo, Qi Quan; Huang, Shou Guo; Li, Yi De

2016-10-01

An optimization strategy combining global semi-empirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (InSb)n clusters with n = 6-10. A new structural growth pattern of the clusters was observed. The lowest energy structures of (InSb)6 and (InSb)8 were different from that of previously reported results. Competition existed between core-shell and cage-like structures of (InSb)8. The structural transition of (InSb)n clusters occurred at size n = 8-9. For (InSb)9 and (InSb)10 clusters, core-shell structure were more energetically favorable than the cage. The corresponding electronic properties were investigated.

Ligand induced structural isomerism in phosphine coordinated gold clusters revealed by ion mobility mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ligare, Marshall R.; Baker, Erin S.; Laskin, Julia

Structural isomerism in ligated gold clusters is revealed using electrospray ionization ion mobility spectrometry mass spectrometry. Phosphine ligated Au8 clusters are shown to adopt more “extended” type structures with increasing exchange of methyldiphenylphosphine (MePPh2) for triphenylphosphine (PPh3). These ligand-dependant structure-property relationships are critical to applications of clusters in catalysis.

Laser-driven deflection arrangements and methods involving charged particle beams

DOEpatents

Plettner, Tomas [San Ramon, CA; Byer, Robert L [Stanford, CA

2011-08-09

Systems, methods, devices and apparatus are implemented for producing controllable charged particle beams. In one implementation, an apparatus provides a deflection force to a charged particle beam. A source produces an electromagnetic wave. A structure, that is substantially transparent to the electromagnetic wave, includes a physical structure having a repeating pattern with a period L and a tilted angle .alpha., relative to a direction of travel of the charged particle beam, the pattern affects the force of the electromagnetic wave upon the charged particle beam. A direction device introduces the electromagnetic wave to the structure to provide a phase-synchronous deflection force to the charged particle beam.

Transmission of cluster ions through a tandem accelerator of several stripper gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saitoh, Yuichi; Chiba, Atsuya; Narumi, Kazumasa

2009-10-15

The transmissions of carbon cluster ion beams through a tandem accelerator using several stripper gases (He, N{sub 2}, CO{sub 2}, and SF{sub 6}) with a terminal voltage of 2.5 MV were measured as a function of the gas pressure in investigating the most suitable gas for cluster ion acceleration. This resulted in it being demonstrated that the highest transmission could be obtained using the smaller size gas, i.e., helium displayed the best performance of the four gases used. In addition, the ratio of transmissions of C{sub n} with helium and nitrogen increased with increases in the n, thus revealing thatmore » helium gas should prove the most effective in larger cluster ion acceleration using the same energy.« less

Retrofitting of Reinforced Concrete Beams using Reactive Powder Concrete (RPC)

NASA Astrophysics Data System (ADS)

Karthik, S.; Sundaravadivelu, Karthik

2017-07-01

Strengthening of existing damaged structures is one of the leading studies in civil engineering. The purpose of retrofitting is to structurally treat the member with an aim to restore the structure to its original strength. The focus of this project is to study the behaviour of damaged Reinforced Concrete beam retrofitted with Reactive Powder Concrete (RPC) Overlay. Reinforced concrete beams of length 1200 mm, width 100 mm and depth 200 mm were casted with M30 grade of concrete in the laboratory and cured for 28 days. One beam is taken as control and are tested under two point loading to find out ultimate load. Remaining beams are subjected to 90 % ultimate load of control beams. The partially damaged beams are retrofitted with Reactive Powder Concrete Overlay at the full tension face of the beam and side overlay depends upon the respectable retrofitting techniques with 10 mm and 20 mm thick layer to find optimum. Materials like steel fibres are added to enhance the ductility by eliminating coarse particle for homogeneity of the structure. Finally, the modes of failure for retrofitted beams are analysed experimentally under two point loading & compared the results with Control beam.

bcl::Cluster : A method for clustering biological molecules coupled with visualization in the Pymol Molecular Graphics System.

PubMed

Alexander, Nathan; Woetzel, Nils; Meiler, Jens

2011-02-01

Clustering algorithms are used as data analysis tools in a wide variety of applications in Biology. Clustering has become especially important in protein structure prediction and virtual high throughput screening methods. In protein structure prediction, clustering is used to structure the conformational space of thousands of protein models. In virtual high throughput screening, databases with millions of drug-like molecules are organized by structural similarity, e.g. common scaffolds. The tree-like dendrogram structure obtained from hierarchical clustering can provide a qualitative overview of the results, which is important for focusing detailed analysis. However, in practice it is difficult to relate specific components of the dendrogram directly back to the objects of which it is comprised and to display all desired information within the two dimensions of the dendrogram. The current work presents a hierarchical agglomerative clustering method termed bcl::Cluster. bcl::Cluster utilizes the Pymol Molecular Graphics System to graphically depict dendrograms in three dimensions. This allows simultaneous display of relevant biological molecules as well as additional information about the clusters and the members comprising them.

The structural characteristics of inflatable beams

NASA Astrophysics Data System (ADS)

Wicker, William J.

1992-08-01

Two inflatable beams are designed and fabricated from polyethylene of ultrahigh molecular weight, and the structures are tested against similar composite and metal-alloy tubes. Specific attention is given to the choice of material that insures material stiffness, good strength-to-weight ratio, creep resistance, and durability. A cloth beam is built from a commercial extended-chain polyethylene fiber, and the inflated beams are tested by means of three- and four-point loading to measure bending and shear deformation. Comparing geometrically similar structures shows that the fabric beams can be about 35 percent as stiff as aluminum for small deflections. The inflatable beams have elastic stiffness coefficients five and two times higher than those for nylon and polyester tubes, respectively. Inflatable structures are concluded to hold promise for lightweight aerospace applications which demand small storage areas.

Generation of tunable radially polarized array beams by controllable coherence

NASA Astrophysics Data System (ADS)

Wang, Jing; Zhang, Jipeng; Zhu, Shijun; Li, Zhenhua

2017-05-01

In this paper, a new method for converting a single radial polarization beam into an arbitrary radially polarized array (RPA) beam such as a radial or rectangular symmetry array in the focal plane by modulating a periodic correlation structure is introduced. The realizability conditions for such source and the beam condition for radiation generated by such source are derived. It is illustrated that both the amplitude and the polarization are controllable by means of initial correlation structure and coherence parameter. Furthermore, by designing the source correlation structure, a tunable NUST-shaped RPA beam is demonstrated, which can find widespread applications in micro-nano engineering. Such a method for generation of arbitrary vector array beams is useful in beam shaping and optical tweezers.

Analysis of truss, beam, frame, and membrane components. [composite structures

NASA Technical Reports Server (NTRS)

Knoell, A. C.; Robinson, E. Y.

1975-01-01

Truss components are considered, taking into account composite truss structures, truss analysis, column members, and truss joints. Beam components are discussed, giving attention to composite beams, laminated beams, and sandwich beams. Composite frame components and composite membrane components are examined. A description is given of examples of flat membrane components and examples of curved membrane elements. It is pointed out that composite structural design and analysis is a highly interactive, iterative procedure which does not lend itself readily to characterization by design or analysis function only.-

Characterization of fundamental catalytic properties of MoS2/WS2 nanotubes and nanoclusters for desulfurization catalysis - a surface temperature study

DOE Office of Scientific and Technical Information (OSTI.GOV)

U. Burghaus

2012-07-05

The prior project consisted of two main project lines. First, characterization of novel nanomaterials for hydrodesulfurization (HDS) applications. Second, studying more traditional model systems for HDS such as vapor-deposited silica-supported Mo and MoSx clusters. In the first subproject, we studied WS2 and MoS2 fullerene-like nanoparticles as well as WS2 nanotubes. Thiophene (C4H4S) was used as the probe molecule. Interestingly, metallic and sulfur-like adsorption sites could be identified on the silica-supported fullerene-particles system. Similar structures are seen for the traditional system (vapor-deposited clusters). Thus, this may be a kinetics fingerprint feature of modern HDS model systems. In addition, kinetics data allowedmore » characterization of the different adsorption sites for thiophene on and inside WS2 nanotube bundles. The latter is a unique feature of nanotubes that has not been reported before for any inorganic nanotube system; however, examples are known for carbon nanotubes, including prior work of the PI. Although HDS has been studied for decades, utilizing nanotubes as nanosized HDS reactors has never been tried before, as far as we know. This is of interest from a fundamental perspective. Unfortunately, the HDS activity of the nanocatalysts at ultra-high vacuum (UHV) conditions was close to the detection limit of our techniques. Therefore, we propose to run experiments at ambient pressure on related nanopowder samples as part of the renewal application utilizing a now-available GC (gas chromatograph) setup. In addition, Ni and Co doped nanocatalyts are proposed for study. These dopants will boost the catalytic activity. In the second subproject of the prior grant, we studied HDS-related chemistry on more traditional supported cluster catalysts. Mo clusters supported by physical vapor deposition (PVD) on silica have been characterized. Two reaction pathways are evident when adsorbing thiophene on Mo and MoSx clusters: molecular adsorption and dissociation. PVD Mo clusters turned out to be very reactive toward thiophene bond activation. Sulfur and carbon residuals form, which poison the catalyst and sulfide the Mo clusters. Sulfided silica-supported MoSx samples are not reactive toward thiophene bond activation. In addition to S and C deposits, H2, H2S, and small organic molecules were detected in the gas phase. Catalyst reactivation procedures, including O2 and atomic hydrogen treatments, have been tested. Cluster size effects have been seen: thiophene adsorbs molecularly with larger binding energies on smaller clusters. However, larger clusters have smaller activation energy for C4H4S bond activation than smaller clusters. The latter is consistent with early catalysis studies. Kinetics and dynamics parameters have been determined quantitatively. We spent a significant amount of time on upgrades of our equipment. A 2nd-hand refurbished X-ray photoelectron spectrometer (XPS) has been integrated into the existing molecular beam scattering system and is already operational (supported by the DoE supplemental grant available in October 2009). We also added a time of flight (TOF) system to the beam scattering apparatus and improved on the accessible impact energy range (new nozzle heater and gas mixing manifold) for the beam scattering experiments. In addition, a GC-based powder atmospheric flow reactor for studies on powder samples is now operational. Furthermore, a 2nd UHV kinetics system has been upgraded as well. In summary, mostly single crystal systems have so far been considered in basic science studies about HDS. Industrial catalysts, however, can be better approximated with the supported cluster systems that we studied in this project. Furthermore, an entirely new class of HDS systems, namely fullerene-like particles and inorganic nanotubes, has been included. Studying new materials and systems has the potential to impact science and technology. The systems investigated are closely related to energy and environmental-related surface science/catalysis. This prior project, conducted at NDSU by a small team, resulted in a total of 14 printed publications,1-5, 7-12, 14, 19, 20eight months before the end of the funding period. In addition, collaborators at national laboratories and abroad were part of the projects, as proposed. More specifically, projects about HDS on MoS2 and WS2 inorganic fullerene-like nanoparticles,1, 5 inorganic WS2 nanotubes,2 Mo and MoS2 vapor-deposited nanoclusters,3 modeling,19 reviews/book chapter,7, 11 and side projects8-10 have been conducted, as proposed, acknowledging solely (exception ref.7) funding from this grant. A list of publications and coworkers is given in sect. 6.« less

The Swift AGN and Cluster Survey

NASA Astrophysics Data System (ADS)

Dai, Xinyu

A key question in astrophysics is to constrain the evolution of the largest gravitationally bound structures in the universe. The serendipitous observations of Swift-XRT form an excellent medium-deep and wide soft X-ray survey, with a sky area of 160 square degrees at the flux limit of 5e-15 erg/s/cm^2. This survey is about an order of magnitude deeper than previous surveys of similar areas, and an order of magnitude wider than previous surveys of similar depth. It is comparable to the planned eROSITA deep survey, but already with the data several years ahead. The unique combination of the survey area and depth enables it to fill in the gap between the deep, pencil beam surveys (such as the Chandra Deep Fields) and the shallow, wide area surveys measured with ROSAT. With it, we will place independent and complementary measurements on the number counts and luminosity functions of X-ray sources. It has been proved that this survey is excellent for X-ray selected galaxy cluster surveys, based on our initial analysis of 1/4 of the fields and other independent studies. The highest priority goal is to produce the largest, uniformly selected catalog of X-ray selected clusters and increase the sample of intermediate to high redshift clusters (z > 0.5) by an order of magnitude. From this catalog, we will study the evolution of cluster number counts, luminosity function, scaling relations, and eventually the mass function. For example, various smaller scale surveys concluded divergently on the evolution of a key scaling relation, between temperature and luminosity of clusters. With the statistical power from this large sample, we will resolve the debate whether clusters evolve self-similarly. This is a crucial step in mapping cluster evolution and constraining cosmological models. First, we propose to extract the complete serendipitous extended source list for all Swift-XRT data to 2015. Second, we will use optical/IR observations to further identify galaxy clusters. These optical/IR observations include data from the SDSS, WISE, and deep optical follow-up observations from the APO, MDM, Magellan, and NOAO telescopes. WISE will confirm all z0.5 clusters. We will use ground-based observations to measure redshifts for z>0.5 clusters, with a focus of measuring 1/10 of the spectroscopic redshifts of z>0.5 clusters within the budget period. Third, we will analyze our deep Suzaku Xray follow-up observations of a sample of medium redshift clusters, and the 1/10 bright Swift clusters suitable for spectral analysis. We will also perform stacking analysis using the Swift data for clusters in different redshift bins to constrain the evolution of cluster properties.

Theoretical prediction of a new stable structure of Au28(SR)20 cluster

NASA Astrophysics Data System (ADS)

Sun, Xiangxiang; Wang, Pu; Xiong, Lin; Pei, Yong

2018-07-01

A new stable structure of Au28(SR)20 cluster is predicted, which has the same gold core as two known structures but different Au-S framework. The new Au28(SR)20 cluster is proposed to be a key link in the evolution of Au22(SR)18, Au34(SR)22 and Au40(SR)24 clusters. The four clusters belong to a homogenous Au16+6N(SR)16+2N series (N = 1-4). The relative stabilities of the new Au28 isomer structure were confirmed by density functional theory calculations including dispersion corrections (DFT-D). It is found that upon protection of certain SR ligands, the new isomer structure has lower or comparable energies to two known cluster structures.

Soft- and reactive landing of ions onto surfaces: Concepts and applications: CONCEPTS AND APPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Grant E.; Gunaratne, Don; Laskin, Julia

2015-04-16

Soft- and reactive landing of mass-selected ions is gaining attention as a promising approach for the precisely-controlled preparation of materials on surfaces that are not amenable to deposition using conventional methods. A broad range of ionization sources and mass-filters are available that make ion soft-landing a versatile tool for surface modification using beams of hyperthermal (< 100 eV) ions. The ability to select the mass-to-charge ratio of the ion, its kinetic energy and charge state, along with precise control of the size, shape, and position of the ion beam on the deposition target distinguishes ion soft landing from other surfacemore » modification techniques. Soft- and reactive landing have been used to prepare interfaces for practical applications as well as precisely-defined model surfaces for fundamental investigations in chemistry, physics, and materials science. For instance, soft- and reactive landing have been applied to study the surface chemistry of ions isolated in the gas-phase, prepare arrays of proteins for high-throughput biological screening, produce novel carbon-based and polymer materials, enrich the secondary structure of peptides and the chirality of organic molecules, immobilize electrochemically-active proteins and organometallics on electrodes, create thin films of complex molecules, and immobilize catalytically active organometallics as well as ligated metal clusters. In addition, soft landing has enabled investigation of the size-dependent behavior of bare metal clusters in the critical subnanometer size regime where chemical and physical properties do not scale predictably with size. The morphology, aggregation, and immobilization of larger bare metal nanoparticles, which are directly relevant to the design of catalysts as well as improved memory and electronic devices, have also been studied using ion soft landing. This review article begins in section 1 with a brief introduction to the existing applications of ion soft- and reactive landing. Section 2 provides an overview of the ionization sources and mass filters that have been used to date for soft landing of mass-selected ions. A discussion of the competing processes that occur during ion deposition as well as the types of ions and surfaces that have been investigated follows in section 3. Section 4 discusses the physical phenomena that occur during and after ion soft landing including retention and reduction of ionic charge along with factors that impact the efficiency of ion deposition. The influence of soft landing on the secondary structure and biological activity of complex ions is addressed in section 5. Lastly, an overview of the structure and mobility as well as the catalytic, optical, magnetic, and redox properties of bare ionic clusters and nanoparticles deposited onto surfaces is presented in section 6.« less

Down-to-earth studies of carbon clusters

NASA Technical Reports Server (NTRS)

Smalley, R. E.

1990-01-01

Recent advances in supersonic beam experiments with laser-vaporization sources of clusters have provided some interesting new insights into the nature of the small clusters of carbon, and the processes through which carbon condenses. One cluster in particular, C(sub 60), appears to play a central role. It is argued that this cluster takes the shape of a soccerball: a hollow sphere composed of a shell of 60 carbon atoms connected by a lattice of hexagonal and pentagonal rings, in a pattern of overall icosahedral symmetry. Although C(sub 60) appears to be uniquely stable due to its perfect symmetry, all other even-numbered carbon clusters in the 32 to 100+ atom size range seem to favor similar closed spheroidal forms. These species are interpreted as relatively unreactive side products in condensation reactions of carbon vapor involving spiraling graphitic sheets. The prevalence of C(sub 60) in laser-vaporized carbon vapors and sooting flames suggests that it may be formed readily whenever carbon condenses. Such ready formation and extraordinary stability may have substantial astrophysical implications.

Down-to-earth studies of carbon clusters

NASA Astrophysics Data System (ADS)

Smalley, R. E.

1990-04-01

Recent advances in supersonic beam experiments with laser-vaporization sources of clusters have provided some interesting new insights into the nature of the small clusters of carbon, and the processes through which carbon condenses. One cluster in particular, C60, appears to play a central role. It is argued that this cluster takes the shape of a soccer ball: a hollow sphere composed of a shell of 60 carbon atoms connected by a lattice of hexagonal and pentagonal rings, in a pattern of overall icosahedral symmetry. Although C60 appears to be uniquely stable due to its perfect symmetry, all other even-numbered carbon clusters in the 32 to 100+ atom size range seem to favor similar closed spheroidal forms. These species are interpreted as relatively unreactive side products in condensation reactions of carbon vapor involving spiraling graphitic sheets. The prevalence of C60 in laser-vaporized carbon vapors and sooting flames suggests that it may be formed readily whenever carbon condenses. Such ready formation and extraordinary stability may have substantial astrophysical implications.

Visualizing and Clustering Protein Similarity Networks: Sequences, Structures, and Functions.

PubMed

Mai, Te-Lun; Hu, Geng-Ming; Chen, Chi-Ming

2016-07-01

Research in the recent decade has demonstrated the usefulness of protein network knowledge in furthering the study of molecular evolution of proteins, understanding the robustness of cells to perturbation, and annotating new protein functions. In this study, we aimed to provide a general clustering approach to visualize the sequence-structure-function relationship of protein networks, and investigate possible causes for inconsistency in the protein classifications based on sequences, structures, and functions. Such visualization of protein networks could facilitate our understanding of the overall relationship among proteins and help researchers comprehend various protein databases. As a demonstration, we clustered 1437 enzymes by their sequences and structures using the minimum span clustering (MSC) method. The general structure of this protein network was delineated at two clustering resolutions, and the second level MSC clustering was found to be highly similar to existing enzyme classifications. The clustering of these enzymes based on sequence, structure, and function information is consistent with each other. For proteases, the Jaccard's similarity coefficient is 0.86 between sequence and function classifications, 0.82 between sequence and structure classifications, and 0.78 between structure and function classifications. From our clustering results, we discussed possible examples of divergent evolution and convergent evolution of enzymes. Our clustering approach provides a panoramic view of the sequence-structure-function network of proteins, helps visualize the relation between related proteins intuitively, and is useful in predicting the structure and function of newly determined protein sequences.

Ligand-protected gold clusters: the structure, synthesis and applications

NASA Astrophysics Data System (ADS)

Pichugina, D. A.; Kuz'menko, N. E.; Shestakov, A. F.

2015-11-01

Modern concepts of the structure and properties of atomic gold clusters protected by thiolate, selenolate, phosphine and phenylacetylene ligands are analyzed. Within the framework of the superatom theory, the 'divide and protect' approach and the structure rule, the stability and composition of a cluster are determined by the structure of the cluster core, the type of ligands and the total number of valence electrons. Methods of selective synthesis of gold clusters in solution and on the surface of inorganic composites based, in particular, on the reaction of Aun with RS, RSe, PhC≡C, Hal ligands or functional groups of proteins, on stabilization of clusters in cavities of the α-, β and γ-cyclodextrin molecules (Au15 and Au25) and on anchorage to a support surface (Au25/SiO2, Au20/C, Au10/FeOx) are reviewed. Problems in this field are also discussed. Among the methods for cluster structure prediction, particular attention is given to the theoretical approaches based on the density functional theory (DFT). The structures of a number of synthesized clusters are described using the results obtained by X-ray diffraction analysis and DFT calculations. A possible mechanism of formation of the SR(AuSR)n 'staple' units in the cluster shell is proposed. The structure and properties of bimetallic clusters MxAunLm (M=Pd, Pt, Ag, Cu) are discussed. The Pd or Pt atom is located at the centre of the cluster, whereas Ag and Cu atoms form bimetallic compounds in which the heteroatom is located on the surface of the cluster core or in the 'staple' units. The optical properties, fluorescence and luminescence of ligand-protected gold clusters originate from the quantum effects of the Au atoms in the cluster core and in the oligomeric SR(AuSR)x units in the cluster shell. Homogeneous and heterogeneous reactions catalyzed by atomic gold clusters are discussed in the context of the reaction mechanism and the nature of the active sites. The bibliography includes 345 references.

GENERAL: Teleportation of a Bipartite Entangled Coherent State via a Four-Partite Cluster-Type Entangled State

NASA Astrophysics Data System (ADS)

Chen, Hui-Na; Liu, Jin-Ming

2009-10-01

We present an optical scheme to almost completely teleport a bipartite entangled coherent state using a four-partite cluster-type entangled coherent state as quantum channel. The scheme is based on optical elements such as beam splitters, phase shifters, and photon detectors. We also obtain the average fidelity of the teleportation process. It is shown that the average fidelity is quite close to unity if the mean photon number of the coherent state is not too small.

CHIMERA: Top-down model for hierarchical, overlapping and directed cluster structures in directed and weighted complex networks

NASA Astrophysics Data System (ADS)

Franke, R.

2016-11-01

In many networks discovered in biology, medicine, neuroscience and other disciplines special properties like a certain degree distribution and hierarchical cluster structure (also called communities) can be observed as general organizing principles. Detecting the cluster structure of an unknown network promises to identify functional subdivisions, hierarchy and interactions on a mesoscale. It is not trivial choosing an appropriate detection algorithm because there are multiple network, cluster and algorithmic properties to be considered. Edges can be weighted and/or directed, clusters overlap or build a hierarchy in several ways. Algorithms differ not only in runtime, memory requirements but also in allowed network and cluster properties. They are based on a specific definition of what a cluster is, too. On the one hand, a comprehensive network creation model is needed to build a large variety of benchmark networks with different reasonable structures to compare algorithms. On the other hand, if a cluster structure is already known, it is desirable to separate effects of this structure from other network properties. This can be done with null model networks that mimic an observed cluster structure to improve statistics on other network features. A third important application is the general study of properties in networks with different cluster structures, possibly evolving over time. Currently there are good benchmark and creation models available. But what is left is a precise sandbox model to build hierarchical, overlapping and directed clusters for undirected or directed, binary or weighted complex random networks on basis of a sophisticated blueprint. This gap shall be closed by the model CHIMERA (Cluster Hierarchy Interconnection Model for Evaluation, Research and Analysis) which will be introduced and described here for the first time.

Chirally directed formation of nanometer-scale proline clusters.

PubMed

Myung, Sunnie; Fioroni, Marco; Julian, Ryan R; Koeniger, Stormy L; Baik, Mu-Hyun; Clemmer, David E

2006-08-23

Ion mobility measurements, combined with molecular mechanics simulations, are used to study enantiopure and racemic proline clusters formed by electrospray ionization. Broad distributions of cluster sizes and charge states are observed, ranging from clusters containing only a few proline units to clusters that contain more than 100 proline units (i.e., protonated clusters of the form [xPro + nH](n+) with x = 1 to >100 and n = 1-7). As the sizes of clusters increase, there is direct evidence for nanometer scale, chirally induced organization into specific structures. For n = 4 and 5, enantiopure clusters of approximately 50 to 100 prolines assemble into structures that are more elongated than the most compact structure that is observed from the racemic proline clusters. A molecular analogue, cis-4-hydroxy-proline, displays significantly different behavior, indicating that in addition to the rigidity of the side chain ring, intermolecular interactions are important in the formation of chirally directed clusters. This is the first case in which assemblies of chirally selective elongated structures are observed in this size range of amino acid clusters. Relationships between enantiopurity, cluster shape, and overall energetics are discussed.

Beyond Low-Rank Representations: Orthogonal clustering basis reconstruction with optimized graph structure for multi-view spectral clustering.

PubMed

Wang, Yang; Wu, Lin

2018-07-01

Low-Rank Representation (LRR) is arguably one of the most powerful paradigms for Multi-view spectral clustering, which elegantly encodes the multi-view local graph/manifold structures into an intrinsic low-rank self-expressive data similarity embedded in high-dimensional space, to yield a better graph partition than their single-view counterparts. In this paper we revisit it with a fundamentally different perspective by discovering LRR as essentially a latent clustered orthogonal projection based representation winged with an optimized local graph structure for spectral clustering; each column of the representation is fundamentally a cluster basis orthogonal to others to indicate its members, which intuitively projects the view-specific feature representation to be the one spanned by all orthogonal basis to characterize the cluster structures. Upon this finding, we propose our technique with the following: (1) We decompose LRR into latent clustered orthogonal representation via low-rank matrix factorization, to encode the more flexible cluster structures than LRR over primal data objects; (2) We convert the problem of LRR into that of simultaneously learning orthogonal clustered representation and optimized local graph structure for each view; (3) The learned orthogonal clustered representations and local graph structures enjoy the same magnitude for multi-view, so that the ideal multi-view consensus can be readily achieved. The experiments over multi-view datasets validate its superiority, especially over recent state-of-the-art LRR models. Copyright © 2018 Elsevier Ltd. All rights reserved.

Evolution of the secondary electron emission during the graphitization of thin C films

NASA Astrophysics Data System (ADS)

Larciprete, Rosanna; Grosso, Davide Remo; Di Trolio, Antonio; Cimino, Roberto

2015-02-01

The relation between the atomic hybridization and the secondary electron emission yield (SEY) in carbon materials has been investigated during the thermal graphitization of thin amorphous carbon layers deposited by magnetron sputtering on Cu substrates. C1s core level, valence band and Raman spectroscopy were used to follow the sp3→sp2 structural reorganization while the SEY curves as a function of the kinetic energy of the incident electron beam were measured in parallel. We found that an amorphous C layer with a thickness of a few tens of nanometers is capable to modify the secondary emission properties of the clean copper surface, reducing the maximum yield from 1.4 to 1.2. A further SEY decrease observed with the progressive conversion of sp3 hybrids into six-fold aromatic domains was related to the electronic structure close to the Fermi level of the C-films. We found that a moderate structural quality of the C layer is sufficient to notably decrease the SEY as aromatic clusters of limited size approach the secondary emission properties of graphite.

SAFT-assisted sound beam focusing using phased arrays (PA-SAFT) for non-destructive evaluation

NASA Astrophysics Data System (ADS)

Nanekar, Paritosh; Kumar, Anish; Jayakumar, T.

2015-04-01

Focusing of sound has always been a subject of interest in ultrasonic non-destructive evaluation. An integrated approach to sound beam focusing using phased array and synthetic aperture focusing technique (PA-SAFT) has been developed in the authors' laboratory. The approach involves SAFT processing on ultrasonic B-scan image collected by a linear array transducer using a divergent sound beam. The objective is to achieve sound beam focusing using fewer elements than the ones required using conventional phased array. The effectiveness of the approach is demonstrated on aluminium blocks with artificial flaws and steel plate samples with embedded volumetric weld flaws, such as slag and clustered porosities. The results obtained by the PA-SAFT approach are found to be comparable to those obtained by conventional phased array and full matrix capture - total focusing method approaches.

Probing the Structures and Electronic Properties of Dual-Phosphorus-Doped Gold Cluster Anions (AunP-2, n = 1–8): A Density functional Theory Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Kang-Ming; Huang, Teng; Liu, Yi-Rong

2015-07-29

The geometries of gold clusters doped with two phosphorus atoms, (AunP-2, n = 1–8) were investigated using density functional theory (DFT) methods. Various two-dimensional (2D) and three-dimensional (3D) structures of the doped clusters were studied. The results indicate that the structures of dual-phosphorus-doped gold clusters exhibit large differences from those of pure gold clusters with small cluster sizes. In our study, as for Au6P-2, two cis–trans isomers were found. The global minimum of Au8P-2 presents a similar configuration to that of Au-20, a pyramid-shaped unit, and the potential novel optical and catalytic properties of this structure warrant further attention. Themore » higher stability of AunP-2 clusters relative to Au-n+2 (n = 1–8) clusters was verified based on various energy parameters, and the results indicate that the phosphorus atom can improve the stabilities of the gold clusters. We then explored the evolutionary path of (n = 1–8) clusters. We found that AunP-2 clusters exhibit the 2D–3D structural transition at n = 6, which is much clearer and faster than that of pure gold clusters and single-phosphorus-doped clusters. The electronic properties of AunP-2 (n = 1–8) were then investigated. The photoelectron spectra provide additional fundamental information on the structures and molecular orbitals shed light on the evolution of AunP-2 (n = 1–8). Natural bond orbital (NBO) described the charge distribution in stabilizing structures and revealed the strong relativistic effects of the gold atoms.« less

Two worlds collide: Image analysis methods for quantifying structural variation in cluster molecular dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steenbergen, K. G., E-mail: kgsteen@gmail.com; Gaston, N.

2014-02-14

Inspired by methods of remote sensing image analysis, we analyze structural variation in cluster molecular dynamics (MD) simulations through a unique application of the principal component analysis (PCA) and Pearson Correlation Coefficient (PCC). The PCA analysis characterizes the geometric shape of the cluster structure at each time step, yielding a detailed and quantitative measure of structural stability and variation at finite temperature. Our PCC analysis captures bond structure variation in MD, which can be used to both supplement the PCA analysis as well as compare bond patterns between different cluster sizes. Relying only on atomic position data, without requirement formore » a priori structural input, PCA and PCC can be used to analyze both classical and ab initio MD simulations for any cluster composition or electronic configuration. Taken together, these statistical tools represent powerful new techniques for quantitative structural characterization and isomer identification in cluster MD.« less

Two worlds collide: image analysis methods for quantifying structural variation in cluster molecular dynamics.

PubMed

Steenbergen, K G; Gaston, N

2014-02-14

Inspired by methods of remote sensing image analysis, we analyze structural variation in cluster molecular dynamics (MD) simulations through a unique application of the principal component analysis (PCA) and Pearson Correlation Coefficient (PCC). The PCA analysis characterizes the geometric shape of the cluster structure at each time step, yielding a detailed and quantitative measure of structural stability and variation at finite temperature. Our PCC analysis captures bond structure variation in MD, which can be used to both supplement the PCA analysis as well as compare bond patterns between different cluster sizes. Relying only on atomic position data, without requirement for a priori structural input, PCA and PCC can be used to analyze both classical and ab initio MD simulations for any cluster composition or electronic configuration. Taken together, these statistical tools represent powerful new techniques for quantitative structural characterization and isomer identification in cluster MD.

Photonic Crystal-Based High-Power Backward Wave Oscillator

DOE PAGES

Poole, Brian R.; Harris, John R.

2017-12-01

An electron beam traversing a slow wave structure can be used to either generate or amplify electromagnetic radiation through the interaction of the slow space charge wave on the beam with the slow wave structure modes. Here, a cylindrical waveguide with a periodic array of conducting loops is used for the slow wave structure. This paper considers operation as a backward wave oscillator. The dispersion properties of the structure are determined using a frequency-domain eigenmode solver. The interaction of the electron beam with the structure modes is investigated using a 2-D particle-in-cell (PIC) code. In conclusion, the operating frequency andmore » growth rate dependence on beam energy and beam current are investigated using the PIC code and compared with analytic and scaling estimates where possible.« less

Photonic Crystal-Based High-Power Backward Wave Oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poole, Brian R.; Harris, John R.

An electron beam traversing a slow wave structure can be used to either generate or amplify electromagnetic radiation through the interaction of the slow space charge wave on the beam with the slow wave structure modes. Here, a cylindrical waveguide with a periodic array of conducting loops is used for the slow wave structure. This paper considers operation as a backward wave oscillator. The dispersion properties of the structure are determined using a frequency-domain eigenmode solver. The interaction of the electron beam with the structure modes is investigated using a 2-D particle-in-cell (PIC) code. In conclusion, the operating frequency andmore » growth rate dependence on beam energy and beam current are investigated using the PIC code and compared with analytic and scaling estimates where possible.« less

Direct Femtosecond Laser Surface Structuring with Optical Vortex Beams Generated by a q-plate

PubMed Central

JJ Nivas, Jijil; He, Shutong; Rubano, Andrea; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2015-01-01

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields. PMID:26658307

Research on seismic behavior and filling effect of a new CFT column-CFT beam frame structure

NASA Astrophysics Data System (ADS)

Wang, Ying; Shima, Hiroshi

2009-12-01

Concrete filled-steel tube (CFT) structure is popularly used in practical structures nowadays. Self-compacting concrete (SCC) was employed to construct a new CFT column-CFT beam frame structure (hereinafter cited as new CFT frame structure) in this research. Three specimens, two CFT column-CFT beam joints and one hollow steel column-I beam joint were tested to investigate seismic behavior of the new CFT frame structure. The experimental results showed that SCC can be successfully compacted into the new CFT frame structure joints in the lab, and the joints provided adequate seismic behavior. In order to further assess filling effect of SCC in the long steel tube, scale column-beam subassembly made of acrylics plate was employed and concrete visual model experiment was done. The results showed that the concrete was able to be successfully cast into the subassembly which indicated that the new CFT frame structure is possible to be constructed in the real building.

Research on seismic behavior and filling effect of a new CFT column-CFT beam frame structure

NASA Astrophysics Data System (ADS)

Wang, Ying; Shima, Hiroshi

2010-03-01

Concrete filled-steel tube (CFT) structure is popularly used in practical structures nowadays. Self-compacting concrete (SCC) was employed to construct a new CFT column-CFT beam frame structure (hereinafter cited as new CFT frame structure) in this research. Three specimens, two CFT column-CFT beam joints and one hollow steel column-I beam joint were tested to investigate seismic behavior of the new CFT frame structure. The experimental results showed that SCC can be successfully compacted into the new CFT frame structure joints in the lab, and the joints provided adequate seismic behavior. In order to further assess filling effect of SCC in the long steel tube, scale column-beam subassembly made of acrylics plate was employed and concrete visual model experiment was done. The results showed that the concrete was able to be successfully cast into the subassembly which indicated that the new CFT frame structure is possible to be constructed in the real building.

Structures of undecagold clusters: Ligand effect

NASA Astrophysics Data System (ADS)

Spivey, Kasi; Williams, Joseph I.; Wang, Lichang

2006-12-01

The most stable structure of undecagold, or Au 11, clusters was predicted from our DFT calculations to be planar [L. Xiao, L. Wang, Chem. Phys. Lett. 392 (2004) 452; L. Xiao, B. Tollberg, X. Hu, L. Wang, J. Chem. Phys. 124 (2005) 114309.]. The structures of ligand protected undecagold clusters were shown to be three-dimensional experimentally. In this work, we used DFT calculations to study the ligand effect on the structures of Au 11 clusters. Our results show that the most stable structure of Au 11 is in fact three-dimensional when SCH 3 ligands are attached. This indicates that the structures of small gold clusters are altered substantially in the presence of ligands.

Laser marking on soda-lime glass by laser-induced backside wet etching with two-beam interference

NASA Astrophysics Data System (ADS)

Nakazumi, Tomoka; Sato, Tadatake; Narazaki, Aiko; Niino, Hiroyuki

2016-09-01

For crack-free marking of glass materials, a beam-scanning laser-induced backside wet etching (LIBWE) process by a beam spot with a fine periodic structure was examined. The fine periodic structure was produced within a beam spot by means of a Mach-Zehnder interferometer incorporated to the optical setup for the beam-scanning LIBWE. A fine structure with a period of 9 µm was observed within the microstructures with a diameter of ca. 40 µm fabricated by a laser shot under double-beam irradiation, and they could be homogeneously fabricated within an area of 800  ×  800 µm. The area filled with the microstructures, including fine periodic structures, could be observed in high contrast under a diffuse, on-axis illumination that was used in commercial QR code readers.

Optimum structural sizing of conventional cantilever and joined wing configurations using equivalent beam models

NASA Technical Reports Server (NTRS)

Hajela, P.; Chen, J. L.

1986-01-01

The present paper describes an approach for the optimum sizing of single and joined wing structures that is based on representing the built-up finite element model of the structure by an equivalent beam model. The low order beam model is computationally more efficient in an environment that requires repetitive analysis of several trial designs. The design procedure is implemented in a computer program that requires geometry and loading data typically available from an aerodynamic synthesis program, to create the finite element model of the lifting surface and an equivalent beam model. A fully stressed design procedure is used to obtain rapid estimates of the optimum structural weight for the beam model for a given geometry, and a qualitative description of the material distribution over the wing structure. The synthesis procedure is demonstrated for representative single wing and joined wing structures.

Ensemble clustering in visual working memory biases location memories and reduces the Weber noise of relative positions.

PubMed

Lew, Timothy F; Vul, Edward

2015-01-01

People seem to compute the ensemble statistics of objects and use this information to support the recall of individual objects in visual working memory. However, there are many different ways that hierarchical structure might be encoded. We examined the format of structured memories by asking subjects to recall the locations of objects arranged in different spatial clustering structures. Consistent with previous investigations of structured visual memory, subjects recalled objects biased toward the center of their clusters. Subjects also recalled locations more accurately when they were arranged in fewer clusters containing more objects, suggesting that subjects used the clustering structure of objects to aid recall. Furthermore, subjects had more difficulty recalling larger relative distances, consistent with subjects encoding the positions of objects relative to clusters and recalling them with magnitude-proportional (Weber) noise. Our results suggest that clustering improved the fidelity of recall by biasing the recall of locations toward cluster centers to compensate for uncertainty and by reducing the magnitude of encoded relative distances.

Periodic permanent magnet focused klystron

DOEpatents

Ferguson, Patrick; Read, Michael; Ives, R Lawrence

2015-04-21

A periodic permanent magnet (PPM) klystron has beam transport structures and RF cavity structures, each of which has permanent magnets placed substantially equidistant from a beam tunnel formed about the central axis, and which are also outside the extent of a cooling chamber. The RF cavity sections also have permanent magnets which are placed substantially equidistant from the beam tunnel, but which include an RF cavity coupling to the beam tunnel for enhancement of RF carried by an electron beam in the beam tunnel.

Thermoelectric properties of Zn4Sb3/CeFe(4-x)CoxSb12 nano-layered superlattices modified by MeV Si ion beam

NASA Astrophysics Data System (ADS)

Budak, S.; Guner, S.; Minamisawa, R. A.; Muntele, C. I.; Ila, D.

2014-08-01

We prepared multilayers of superlattice thin film system with 50 periodic alternating nano-layers of semiconducting half-Heusler β-Zn4Sb3 and skutterudite CeFe2Co2Sb12 compound thin films using ion beam assisted deposition (IBAD) with Au layers deposited on both sides as metal contacts. The deposited multilayer thin films have alternating layers about 5 nm thick. The total thickness of the multilayer system is 275 nm. The superlattices were then bombarded by 5 MeV Si ion at six different fluences to form nano-cluster structures. The film thicknesses and composition were monitored by Rutherford backscattering spectrometry (RBS) before and after MeV ion bombardment. We have measured the thermoelectric efficiency, Figure of Merit ZT, of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3ω) method, the cross plane Seebeck coefficient, and the electrical conductivity using the van der Pauw method before and after the MeV ion bombardments. We reached the remarkable thermoelectric Figure of Merit results at optimal fluences.

Propagation of modulated electron and X-ray beams through matter and interactions with radio-frequency structures

NASA Astrophysics Data System (ADS)

Harris, J. R.; Miller, R. B.

2018-02-01

The generation and evolution of modulated particle beams and their interactions with resonant radiofrequency (RF) structures are of fundamental interest for both particle accelerator and vacuum electronic systems. When the constraint of propagation in a vacuum is removed, the evolution of such beams can be greatly affected by interactions with matter including scattering, absorption, generation of atmospheric plasma, and the production of multiple generations of secondary particles. Here, we study the propagation of 21 MeV and 25 MeV electron beams produced in S-band and L-band linear accelerators, and their interaction with resonant RF structures, under a number of combinations of geometry, including transmission through both air and metal. Both resonant and nonresonant interactions were observed, with the resonant interactions indicating that the RF modulation on the electron beam is at least partially preserved as the beam propagates through air and metal. When significant thicknesses of metal are placed upstream of a resonant structure, preventing any primary beam electrons from reaching the structure, RF signals could still be induced in the structures. This indicated that the RF modulation present on the electron beam was also impressed onto the x-rays generated when the primary electrons were stopped in the metal, and that this RF modulation was also present on the secondary electrons generated when the x-rays struck the resonant structures. The nature of these interactions and their sensitivities to changes in system configurations will be discussed.

Analysis of the Structures and Properties of (GaSb)n (n = 4-9) Clusters through Density Functional Theory.

PubMed

Lu, Qi Liang; Luo, Qi Quan; Huang, Shou Guo; Li, Yi De; Wan, Jian Guo

2016-07-07

An optimization strategy combining global semiempirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (GaSb)n clusters up to n = 9. The growth pattern of the clusters differed from those of previously reported group III-V binary clusters. A cagelike configuration was found for cluster sizes n ≤ 7. The structure of (GaSb)6 deviated from that of other III-V clusters. Competition existed between core-shell and hollow cage structures of (GaSb)7. Novel noncagelike structures were energetically preferred over the cages for the (GaSb)8 and (GaSb)9 clusters. Electronic properties, such as vertical ionization potential, adiabatic electron affinities, HOMO-LUMO gaps, and average on-site charges on Ga or Sb atoms, as well as binding energies, were computed.

Effect of crack on natural frequency for beam type of structures

NASA Astrophysics Data System (ADS)

Sawant, Saurabh U.; Chauhan, Santosh J.; Deshmukh, Nilaj N.

2017-07-01

Detection of damage in early stages reduces chances of sudden failure of that structure which is important from safety and economic point of view. Crack or damage affects dynamic behavior of structure. In last few decades many researchers have been developing different approaches to detect the damage based on its dynamic behavior. This paper focuses on effect on natural frequency of cantilever beam due to the presence of crack at different locations and with different depths. Cantilever beam is selected for analysis because these beams are most common structures used in many industrial applications. In the present study, modeling of healthy and damaged cantilever beam is done using ANSYSsoftware. Crack at 38 different locations with 1 mm, 2 mm and 3 mm crack depth were created for each of these locations. The effect of these cracks on natural frequency were analyzed over the healthy beam for the first four mode shapes. It is found that the presence of crack decreases the natural frequency of the beam and at some particular locations, the natural frequency of the cracked beam is found to be almost the same as that of the healthy beam.

The Electrical Structure of Discharges Modified by Electron Beams

NASA Astrophysics Data System (ADS)

Haas, F. A.; Braithwaite, N. St. J.

1997-10-01

Injection of an electron beam into a low pressure plasma modifies both the electrical structure and the distributions of charged particle energies. The electrical structure is investigated here in a one-dimensional model by representing the discharge as two collisionless sheaths with a monenergetic electron beam, linked by a quasi-neutral collisional region. The latter is modelled by fluid equations in which the beam current decreases with position. Since the electrodes are connected by an external conductor this implies through Kirchoff's laws that the thermal electron current must correspondingly increase with position. Given the boundary conditions and beam input at the first electrode then the rest of the system is uniquely described. The model reveals the dependence of the sheath potentials at the emitting and absorbing surfaces on the beam current. The model is relevant to externally injected beams and to electron beams originating from secondary processes on surfaces exposed to the plasma.

Cluster beam targets for laser plasma extreme ultraviolet and soft x-ray sources

DOEpatents

Kublak, G.D.; Richardson, M.C.

1996-11-19

Method and apparatus for producing extreme ultraviolet (EUV) and soft x-ray radiation from an ultra-low debris plasma source are disclosed. Targets are produced by the free jet expansion of various gases through a temperature controlled nozzle to form molecular clusters. These target clusters are subsequently irradiated with commercially available lasers of moderate intensity (10{sup 11}--10{sup 12} watts/cm{sup 2}) to produce a plasma radiating in the region of 0.5 to 100 nanometers. By appropriate adjustment of the experimental conditions the laser focus can be moved 10--30 mm from the nozzle thereby eliminating debris produced by plasma erosion of the nozzle. 5 figs.

Cluster beam targets for laser plasma extreme ultraviolet and soft x-ray sources

DOEpatents

Kublak, Glenn D.; Richardson, Martin C. (CREOL

1996-01-01

Method and apparatus for producing extreme ultra violet (EUV) and soft x-ray radiation from an ultra-low debris plasma source are disclosed. Targets are produced by the free jet expansion of various gases through a temperature controlled nozzle to form molecular clusters. These target clusters are subsequently irradiated with commercially available lasers of moderate intensity (10.sup.11 -10.sup.12 watts/cm.sup.2) to produce a plasma radiating in the region of 0.5 to 100 nanometers. By appropriate adjustment of the experimental conditions the laser focus can be moved 10-30 mm from the nozzle thereby eliminating debris produced by plasma erosion of the nozzle.

The [(AI 2O 3) 2] - Anion Cluster: Electron Localization-Delocalization Isomerism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sierka, Marek; Dobler, Jens; Sauer, Joachim

2009-10-05

Three-dimensional bulk alumina and its two-dimensional thin films show great structural diversity, posing considerable challenges to their experimental structural characterization and computational modeling. Recently, structural diversity has also been demonstrated for zerodimensional gas phase aluminum oxide clusters. Mass-selected clusters not only make systematic studies of the structural and electronic properties as a function of size possible, but lately have also emerged as powerful molecular models of complex surfaces and solid catalysts. In particular, the [(Al 2O 3) 3-5] + clusters were the first example of polynuclear maingroup metal oxide cluster that are able to thermally activate CH 4. Over themore » past decades gas phase aluminum oxide clusters have been extensively studied both experimentally and computationally, but definitive structural assignments were made for only a handful of them: the planar [Al 3O 3] - and [Al 5O 4] - cluster anions, and the [(Al 2O 3) 1-4(AlO)] + cluster cations. For stoichiometric clusters only the atomic structures of [(Al 2O 3) 4] +/0 have been nambiguously resolved. Here we report on the structures of the [(Al 2O 3) 2] -/0 clusters combining photoelectron spectroscopy (PES) and quantum chemical calculations employing a genetic algorithm as a global optimization technique. The [(Al 2O 3) 2] - cluster anion show energetically close lying but structurally distinct cage and sheet-like isomers which differ by delocalization/localization of the extra electron. The experimental results are crucial for benchmarking the different computational methods applied with respect to a proper description of electron localization and the relative energies for the isomers which will be of considerable value for future computational studies of aluminum oxide and related systems.« less

Effect of Fe-ion implantation doping on structural and optical properties of CdS thin films

NASA Astrophysics Data System (ADS)

Chandramohan, S.; Kanjilal, A.; Sarangi, S. N.; Majumder, S.; Sathyamoorthy, R.; Som, T.

2010-06-01

We report on effects of Fe implantation doping-induced changes in structural, optical, morphological, and vibrational properties of cadmium sulfide thin films. Films were implanted with 90 keV Fe+ ions at room temperature for a wide range of fluences from 0.1×1016 to 3.6×1016 ions cm-2 (corresponding to 0.38-12.03 at.% of Fe). Glancing angle X-ray diffraction analysis revealed that the implanted Fe atoms tend to supersaturate by occupying the substitutional cationic sites rather than forming metallic clusters or secondary phase precipitates. In addition, Fe doping does not lead to any structural phase transformation although it induces structural disorder and lattice contraction. Optical absorption studies show a reduction in the optical band gap from 2.39 to 2.17 eV with increasing Fe concentration. This is attributed to disorder-induced band tailing in semiconductors and ion-beam-induced grain growth. The strain associated with a lattice contraction is deduced from micro-Raman scattering measurements and is found that size and shape fluctuations of grains, at higher fluences, give rise to inhomogeneity in strain.

Robust and adjustable C-shaped electron vortex beams

NASA Astrophysics Data System (ADS)

Mousley, M.; Thirunavukkarasu, G.; Babiker, M.; Yuan, J.

2017-06-01

Wavefront engineering is an important quantum technology, often applied to the production of states carrying orbital angular momentum (OAM). Here, we demonstrate the design and production of robust C-shaped beam states carrying OAM, in which the usual doughnut-shaped transverse intensity structure of the vortex beam contains an adjustable gap. We find that the presence of the vortex lines in the core of the beam is crucial for maintaining the stability of the C-shape structure during beam propagation. The topological charge of the vortex core controls mainly the size of the C-shape, while its opening angle is related to the presence of vortex-anti-vortex loops. We demonstrate the generation and characterisation of C-shaped electron vortex beams, although the result is equally applicable to other quantum waves. C-shaped electron vortex beams have potential applications in nanoscale fabrication of planar split-ring structures and three-dimensional chiral structures as well as depth sensing and magnetic field determination through rotation of the gap in the C-shape.

Acceleration of on-axis and ring-shaped electron beams in wakefields driven by Laguerre-Gaussian pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Guo-Bo; Key Laboratory for Laser Plasmas; Chen, Min, E-mail: minchen@sjtu.edu.cn, E-mail: yanyunma@126.com

2016-03-14

The acceleration of electron beams with multiple transverse structures in wakefields driven by Laguerre-Gaussian pulses has been studied through three-dimensional (3D) particle-in-cell simulations. Under different laser-plasma conditions, the wakefield shows different transverse structures. In general cases, the wakefield shows a donut-like structure and it accelerates the ring-shaped hollow electron beam. When a lower plasma density or a smaller laser spot size is used, besides the donut-like wakefield, a central bell-like wakefield can also be excited. The wake sets in the center of the donut-like wake. In this case, both a central on-axis electron beam and a ring-shaped electron beam aremore » simultaneously accelerated. Further, reducing the plasma density or laser spot size leads to an on-axis electron beam acceleration only. The research is beneficial for some potential applications requiring special pulse beam structures, such as positron acceleration and collimation.« less

Structural and electronic properties of Aun-xPtx (n = 2-14; x ⩽ n) clusters: The density functional theory investigation

NASA Astrophysics Data System (ADS)

Yuan, H. K.; Kuang, A. L.; Tian, C. L.; Chen, H.

2014-03-01

The structural evolutions and electronic properties of bimetallic Aun-xPtx (n = 2-14; x ⩽ n) clusters are investigated by using the density functional theory (DFT) with the generalized gradient approximation (GGA). The monatomic doping Aun-1Pt clusters are emphasized and compared with the corresponding pristine Aun clusters. The results reveal that the planar configurations are favored for both Aun-1Pt and Aun clusters with size up to n = 13, and the former often employ the substitution patterns based on the structures of the latter. The most stable clusters are Au6 and Au6Pt, which adopt regular planar triangle (D3h) and hexagon-ring (D6h) structures and can be regarded as the preferential building units in designing large clusters. For Pt-rich bimetallic clusters, their structures can be obtained from the substitution of Pt atoms by Au atoms from the Ptn structures, where Pt atoms assemble together and occupy the center yet Au atoms prefer the apex positions showing a segregation effect. With respect to pristine Au clusters, AunPt clusters exhibit somewhat weaker and less pronounced odd-even oscillations in the highest occupied and lowest unoccupied molecular-orbital gaps (HOMO-LUMO gap), electron affinity (EA), and ionization potential (IP) due to the partially released electron pairing effect. The analyses of electronic structure indicate that Pt atoms in AuPt clusters would delocalize their one 6s and one 5d electrons to contribute the electronic shell closure. The sp-d hybridizations as well as the d-d interactions between the host Au and dopant Pt atoms result in the enhanced stabilities of AuPt clusters.

Design and Application of a High Sensitivity Piezoresistive Pressure Sensor for Low Pressure Conditions

PubMed Central

Yu, Huiyang; Huang, Jianqiu

2015-01-01

In this paper, a pressure sensor for low pressure detection (0.5 kPa–40 kPa) is proposed. In one structure (No. 1), the silicon membrane is partly etched to form a crossed beam on its top for stress concentration. An aluminum layer is also deposited as part of the beam. Four piezoresistors are fabricated. Two are located at the two ends of the beam. The other two are located at the membrane periphery. Four piezoresistors connect into a Wheatstone bridge. To demonstrate the stress concentrate effect of this structure, two other structures were designed and fabricated. One is a flat membrane structure (No. 2), the other is a structure with the aluminum beam, but without etched silicon (No. 3). The measurement results of these three structures show that the No.1 structure has the highest sensitivity, which is about 3.8 times that of the No. 2 structure and 2.7 times that of the No. 3 structure. They also show that the residual stress in the beam has some backside effect on the sensor performance. PMID:26371001

Line-of-sight structure toward strong lensing galaxy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayliss, Matthew B.; Johnson, Traci; Sharon, Keren

2014-03-01

We present an analysis of the line-of-sight structure toward a sample of 10 strong lensing cluster cores. Structure is traced by groups that are identified spectroscopically in the redshift range, 0.1 ≤ z ≤ 0.9, and we measure the projected angular and comoving separations between each group and the primary strong lensing clusters in each corresponding line of sight. From these data we measure the distribution of projected angular separations between the primary strong lensing clusters and uncorrelated large-scale structure as traced by groups. We then compare the observed distribution of angular separations for our strong lensing selected lines ofmore » sight against the distribution of groups that is predicted for clusters lying along random lines of sight. There is clear evidence for an excess of structure along the line of sight at small angular separations (θ ≤ 6') along the strong lensing selected lines of sight, indicating that uncorrelated structure is a significant systematic that contributes to producing galaxy clusters with large cross sections for strong lensing. The prevalence of line-of-sight structure is one of several biases in strong lensing clusters that can potentially be folded into cosmological measurements using galaxy cluster samples. These results also have implications for current and future studies—such as the Hubble Space Telescope Frontier Fields—that make use of massive galaxy cluster lenses as precision cosmological telescopes; it is essential that the contribution of line-of-sight structure be carefully accounted for in the strong lens modeling of the cluster lenses.« less

Physics Goals for the Planned Next Linear Collider Engineering Test Facility

NASA Astrophysics Data System (ADS)

Raubenheimer, T. O.

2001-10-01

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well as of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.

Structural, stability, and vibrational properties of BinPm clusters

NASA Astrophysics Data System (ADS)

Shen, Wanting; Han, Lihong; Liang, Dan; Zhang, Chunfang; Ruge, Quhe; Wang, Shumin; Lu, Pengfei

2018-04-01

An in-depth investigation is performed on stability mechanisms, electronic and optical properties of III-V semiconductor vapor phases clusters. First principles electronic structure calculations of CAM-B3LYP are performed on neutral BinPm (n + m ≤ 14) clusters. The geometrical evolution of all stable structures remains amorphous as the clusters size increases. Binding energies (BEs), energy gains and highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO) gaps confirm that all four-atom structures of BinPm clusters have more stable optical properties. Orbitals composition and vibrational spectra of stable clusters are analyzed. Our calculations will contribute to the study of diluted bismuth alloys and compounds.

Hidden electronic rule in the “cluster-plus-glue-atom” model

PubMed Central

Du, Jinglian; Dong, Chuang; Melnik, Roderick; Kawazoe, Yoshiyuki; Wen, Bin

2016-01-01

Electrons and their interactions are intrinsic factors to affect the structure and properties of materials. Based on the “cluster-cluster-plus-glue-atom” model, an electron counting rule for complex metallic alloys (CMAs) has been revealed in this work (i. e. the CPGAMEC rule). Our results on the cluster structure and electron concentration of CMAs with apparent cluster features, indicate that the valence electrons’ number per unit cluster formula for these CMAs are specific constants of eight-multiples and twelve-multiples. It is thus termed as specific electrons cluster formula. This CPGAMEC rule has been demonstrated as a useful guidance to direct the design of CMAs with desired properties, while its practical applications and underlying mechanism have been illustrated on the basis of CMAs’ cluster structural features. Our investigation provides an aggregate picture with intriguing electronic rule and atomic structural features of CMAs. PMID:27642002

Principal Cluster Axes: A Projection Pursuit Index for the Preservation of Cluster Structures in the Presence of Data Reduction

ERIC Educational Resources Information Center

Steinley, Douglas; Brusco, Michael J.; Henson, Robert

2012-01-01

A measure of "clusterability" serves as the basis of a new methodology designed to preserve cluster structure in a reduced dimensional space. Similar to principal component analysis, which finds the direction of maximal variance in multivariate space, principal cluster axes find the direction of maximum clusterability in multivariate space.…

Equilibrium geometries, electronic and magnetic properties of small AunNi- (n = 1-9) clusters

NASA Astrophysics Data System (ADS)

Tang, Cui-Ming; Chen, Xiao-Xu; Yang, Xiang-Dong

2014-05-01

Geometrical, electronic and magnetic properties of small AunNi- (n = 1-9) clusters have been investigated based on density functional theory (DFT) at PW91P86 level. An extensive structural search shows that the relative stable structures of AunNi- (n = 1-9) clusters adopt 2D structure for n = 1-5, 7 and 3D structure for n = 6, 8-9. And the substitution of a Ni atom for an Au atom in the Au-n+1 cluster obviously changes the structure of the host cluster. Moreover, an odd-even alternation phenomenon has been found for HOMO-LUMO energy gaps, indicating that the relative stable structures of the AunNi- clusters with odd-numbered gold atoms have a higher relative stability. Finally, the natural population analysis (NPA) and the vertical detachment energies (VDE) are studied, respectively. The theoretical values of VDE are reported for the first time to our best knowledge.

Atomically precise cluster catalysis towards quantum controlled catalysts

PubMed Central

Watanabe, Yoshihide

2014-01-01

Catalysis of atomically precise clusters supported on a substrate is reviewed in relation to the type of reactions. The catalytic activity of supported clusters has generally been discussed in terms of electronic structure. Several lines of evidence have indicated that the electronic structure of clusters and the geometry of clusters on a support, including the accompanying cluster-support interaction, are strongly correlated with catalytic activity. The electronic states of small clusters would be easily affected by cluster–support interactions. Several studies have suggested that it is possible to tune the electronic structure through atomic control of the cluster size. It is promising to tune not only the number of cluster atoms, but also the hybridization between the electronic states of the adsorbed reactant molecules and clusters in order to realize a quantum-controlled catalyst. PMID:27877723

Bi cluster-assembled interconnects produced using SU8 templates

NASA Astrophysics Data System (ADS)

Partridge, J. G.; Matthewson, T.; Brown, S. A.

2007-04-01

Bi clusters with an average diameter of 25 nm have been deposited from an inert gas aggregation source and assembled into thin-film interconnects which are formed between planar electrical contacts and supported on Si substrates passivated with Si3N4 or thermally grown oxide. A layer of SU8 (a negative photoresist based on EPON SU-8 epoxy resin) is patterned using optical or electron-beam lithography, and it defines the position and dimensions of the cluster film. The conduction between the contacts is monitored throughout the deposition/assembly process, and subsequent I(V) characterization is performed in situ. Bi cluster-assembled interconnects have been fabricated with nanoscale widths and with up to 1:1 thickness:width aspect ratios. The conductivity of these interconnects has been increased, post-deposition, using a simple thermal annealing process.

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

NASA Astrophysics Data System (ADS)

Pohlit, Merlin; Stockem, Irina; Porrati, Fabrizio; Huth, Michael; Schröder, Christian; Müller, Jens

2016-10-01

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamics of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.

Where Water Is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster

PubMed Central

Yano, Junko; Kern, Jan; Sauer, Kenneth; Latimer, Matthew J.; Pushkar, Yulia; Biesiadka, Jacek; Loll, Bernhard; Saenger, Wolfram; Messinger, Johannes; Zouni, Athina; Yachandra, Vittal K.

2014-01-01

The oxidation of water to dioxygen is catalyzed within photosystem II (PSII) by a Mn4Ca cluster, the structure of which remains elusive. Polarized extended x-ray absorption fine structure (EXAFS) measurements on PSII single crystals constrain the Mn4Ca cluster geometry to a set of three similar high-resolution structures. Combining polarized EXAFS and x-ray diffraction data, the cluster was placed within PSII, taking into account the overall trend of the electron density of the metal site and the putative ligands. The structure of the cluster from the present study is unlike either the 3.0 or 3.5 angstrom–resolution x-ray structures or other previously proposed models. PMID:17082458

Investigation of the Structural Behavior and Maximum Bending Strength of Six Multiweb Beams with Three Types of Webs

NASA Technical Reports Server (NTRS)

Peterson, James P.; Bruce, Walter E., Jr.

1959-01-01

The results of bending tests on six multiweb beams of optimum weight-strength design are presented. The internal structure of the beams consisted of various combinations of two types of full-depth solid webs and a post-stringer web. The observed structural behavior, buckling load, and failing load of the beams are compared with results obtained by the use of existing methods of analysis and found to be quite predictable.

Accelerated Electron-Beam Formation with a High Capture Coefficient in a Parallel Coupled Accelerating Structure

NASA Astrophysics Data System (ADS)

Chernousov, Yu. D.; Shebolaev, I. V.; Ikryanov, I. M.

2018-01-01

An electron beam with a high (close to 100%) coefficient of electron capture into the regime of acceleration has been obtained in a linear electron accelerator based on a parallel coupled slow-wave structure, electron gun with microwave-controlled injection current, and permanent-magnet beam-focusing system. The high capture coefficient was due to the properties of the accelerating structure, beam-focusing system, and electron-injection system. Main characteristics of the proposed systems are presented.

A Hierarchical Clustering Methodology for the Estimation of Toxicity

EPA Science Inventory

A Quantitative Structure Activity Relationship (QSAR) methodology based on hierarchical clustering was developed to predict toxicological endpoints. This methodology utilizes Ward's method to divide a training set into a series of structurally similar clusters. The structural sim...

Exploring the atomic structure of 1.8nm monolayer-protected gold clusters with aberration-corrected STEM.

PubMed

Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J; Lahtinen, Tanja; Salorinne, Kirsi; Häkkinen, Hannu; Palmer, Richard E

2017-05-01

Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au 144 (SCH 2 CH 2 Ph) 60 provided by two different research groups. The MP Au clusters were "weighed" by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123-151 atoms, only 3% of clusters matched the theoretically predicted Au 144 (SR) 60 structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters. Copyright © 2017. Published by Elsevier B.V.

Preliminary Analysis of the Aluminiumtimber Composite Beams

NASA Astrophysics Data System (ADS)

Szumigała, Maciej; Chybiński, Marcin; Polus, Łukasz

2017-12-01

This paper presents a new type of composite structures - aluminium-timber beams. These structures have an advantage over other existing composite structures, because they are lighter. However, their application may be limited due to the high price of aluminium alloys. The authors of this article made an attempt to calculate the load-bearing capacity of an aluminium-timber beam.

Calculation of the structure of carbon clusters based on fullerene-like C24 and C48 molecules

NASA Astrophysics Data System (ADS)

Krylova, K. A.; Baimova, Yu. A.; Dmitriev, S. V.; Mulyukov, R. R.

2016-02-01

Equilibrium structures obtained by linking with valence bonds the carbon carcasses of two fullerene-like molecules have been studied by molecular dynamics simulation. In free fullerene, carbon atoms form sp 2 hybridized bonds, but at places of links between fullerenes, sp 3 hybridized bonds are formed, which determines the changes in the properties of such structures. In the literature, the topology of diamond-like phases is described, but equilibrium clusters based on fullerene-like molecules are underexplored. The right angles between the C-C bonds are energetically unfavorable, and the reduction in the energy of clusters in the process of relaxation is connected with the optimization of valence angles, which leads to a reduction in the symmetry of clusters and, in a number of cases, even to disruption of some valence bonds. It is shown that different fashions of linking two fullerenes result in the formation of clusters with different structures and energies. Different initial conditions can lead to different configurations of clusters with the same topology. Among the analyzed clusters, a structure with the minimum potential energy per atom was found. The results of this work contribute to the study of the real structure of carbon clusters.

Structural features of small benzene clusters (C6H6)n (n ≤ 30) as investigated with the all-atom OPLS potential.

PubMed

Takeuchi, Hiroshi

2012-10-18

The structures of the simplest aromatic clusters, benzene clusters (C(6)H(6))(n), are not well elucidated. In the present study, benzene clusters (C(6)H(6))(n) (n ≤ 30) were investigated with the all-atom optimized parameters for liquid simulation (OPLS) potential. The global minima and low-lying minima of the benzene clusters were searched with the heuristic method combined with geometrical perturbations. The structural features and growth sequence of the clusters were examined by carrying out local structure analyses and structural similarity evaluation with rotational constants. Because of the anisotropic interaction between the benzene molecules, the local structures consisting of 13 molecules are considerably deviated from regular icosahedron, and the geometries of some of the clusters are inconsistent with the shapes constructed by the interior molecules. The distribution of the angle between the lines normal to two neighboring benzene rings is anisotropic in the clusters, whereas that in the liquid benzene is nearly isotropic. The geometries and energies of the low-lying configurations and the saddle points between them suggest that most of the configurations previously detected in supersonic expansions take different orientations for one to four neighboring molecules.

The Effects of Environmental Characteristics on the Structure of Hospital Clusters.

ERIC Educational Resources Information Center

Fennell, Mary L.

1980-01-01

The population ecology view that variation in sets or clusters of organizations should be isomorphic with variation in cluster environment was used to explain structural variation among hospital clusters. Cluster differentiation seems to be casually affected by range of services, average hospital size, and the periodic closing of hospitals.…

Multiple co-clustering based on nonparametric mixture models with heterogeneous marginal distributions

PubMed Central

Yoshimoto, Junichiro; Shimizu, Yu; Okada, Go; Takamura, Masahiro; Okamoto, Yasumasa; Yamawaki, Shigeto; Doya, Kenji

2017-01-01

We propose a novel method for multiple clustering, which is useful for analysis of high-dimensional data containing heterogeneous types of features. Our method is based on nonparametric Bayesian mixture models in which features are automatically partitioned (into views) for each clustering solution. This feature partition works as feature selection for a particular clustering solution, which screens out irrelevant features. To make our method applicable to high-dimensional data, a co-clustering structure is newly introduced for each view. Further, the outstanding novelty of our method is that we simultaneously model different distribution families, such as Gaussian, Poisson, and multinomial distributions in each cluster block, which widens areas of application to real data. We apply the proposed method to synthetic and real data, and show that our method outperforms other multiple clustering methods both in recovering true cluster structures and in computation time. Finally, we apply our method to a depression dataset with no true cluster structure available, from which useful inferences are drawn about possible clustering structures of the data. PMID:29049392

Statistical Significance for Hierarchical Clustering

PubMed Central

Kimes, Patrick K.; Liu, Yufeng; Hayes, D. Neil; Marron, J. S.

2017-01-01

Summary Cluster analysis has proved to be an invaluable tool for the exploratory and unsupervised analysis of high dimensional datasets. Among methods for clustering, hierarchical approaches have enjoyed substantial popularity in genomics and other fields for their ability to simultaneously uncover multiple layers of clustering structure. A critical and challenging question in cluster analysis is whether the identified clusters represent important underlying structure or are artifacts of natural sampling variation. Few approaches have been proposed for addressing this problem in the context of hierarchical clustering, for which the problem is further complicated by the natural tree structure of the partition, and the multiplicity of tests required to parse the layers of nested clusters. In this paper, we propose a Monte Carlo based approach for testing statistical significance in hierarchical clustering which addresses these issues. The approach is implemented as a sequential testing procedure guaranteeing control of the family-wise error rate. Theoretical justification is provided for our approach, and its power to detect true clustering structure is illustrated through several simulation studies and applications to two cancer gene expression datasets. PMID:28099990

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltdin situmicro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ~100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face thatmore » preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. Lastly, high-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.« less

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt.

PubMed

Soares, Alexei S; Mullen, Jeffrey D; Parekh, Ruchi M; McCarthy, Grace S; Roessler, Christian G; Jackimowicz, Rick; Skinner, John M; Orville, Allen M; Allaire, Marc; Sweet, Robert M

2014-11-01

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltd in situ micro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ∼100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face that preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. High-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

DOE PAGES

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.; ...

2014-10-09

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltdin situmicro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ~100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face thatmore » preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. Lastly, high-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies.« less

Solvent minimization induces preferential orientation and crystal clustering in serial micro-crystallography on micro-meshes, in situ plates and on a movable crystal conveyor belt

PubMed Central

Soares, Alexei S.; Mullen, Jeffrey D.; Parekh, Ruchi M.; McCarthy, Grace S.; Roessler, Christian G.; Jackimowicz, Rick; Skinner, John M.; Orville, Allen M.; Allaire, Marc; Sweet, Robert M.

2014-01-01

X-ray diffraction data were obtained at the National Synchrotron Light Source from insulin and lysozyme crystals that were densely deposited on three types of surfaces suitable for serial micro-crystallography: MiTeGen MicroMeshes™, Greiner Bio-One Ltd in situ micro-plates, and a moving kapton crystal conveyor belt that is used to deliver crystals directly into the X-ray beam. 6° wedges of data were taken from ∼100 crystals mounted on each material, and these individual data sets were merged to form nine complete data sets (six from insulin crystals and three from lysozyme crystals). Insulin crystals have a parallelepiped habit with an extended flat face that preferentially aligned with the mounting surfaces, impacting the data collection strategy and the design of the serial crystallography apparatus. Lysozyme crystals had a cuboidal habit and showed no preferential orientation. Preferential orientation occluded regions of reciprocal space when the X-ray beam was incident normal to the data-collection medium surface, requiring a second pass of data collection with the apparatus inclined away from the orthogonal. In addition, crystals measuring less than 20 µm were observed to clump together into clusters of crystals. Clustering required that the X-ray beam be adjusted to match the crystal size to prevent overlapping diffraction patterns. No additional problems were encountered with the serial crystallography strategy of combining small randomly oriented wedges of data from a large number of specimens. High-quality data able to support a realistic molecular replacement solution were readily obtained from both crystal types using all three serial crystallography strategies. PMID:25343789

Investigation of the Contribution of Lower Charger State Ar Ions to the Unknown Faint X-Ray Feature Found in the Stacked Spectrum of Galaxy Clusters

NASA Astrophysics Data System (ADS)

Gall, Amy

Driven by the recent detection of an unidentified emission line previously reported at 3.55-3.57 keV in a stacked spectrum of galaxy clusters, in this work we investigated the resonant dielectronic recombination (DR) process in Li-like Ar as a possible source of, or contributor to, the emission line. The Li-like transition 1s22l-1s2l3l' was suggested to produce a 3.62 keV photon [1] near the unidentified line at 3.57 keV and was the primary focus of our study. The Electron Beam Ion Trap at NIST was used to produce and trap the highly-charged ions of argon. The energy of the quasi-monoenergetic electron beam was incremented in steps of 15 eV to scan over all of the Li-like Ar DR resonances. A Johann-type crystal spectrometer and a solid-state germanium detector were used to take x-ray measurements perpendicular to the electron beam. Our broadband results allowed us to identify the processes that produced specific spectral features, while our high-resolution spectra allowed the experimental separation of features that are less than 2 eV apart. We have used the collisional radiative model NOMAD [2] aided by atomic data calculations by FAC [3] to interpret our observations and account for corrections. Experimental results were compared to the atomic database AtomDB, used to fit the galaxy cluster spectra. We found a number of measured features due to DR in lower charge state Ar ions not included in the database, close in energy to the identified line at 3.57 keV, and suggest their inclusion for improved interpretation and diagnosis of other astrophysical spectra.

Photonic guiding structures in lithium niobate crystals produced by energetic ion beams

NASA Astrophysics Data System (ADS)

Chen, Feng

2009-10-01

A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimensions, to realize photonic bandgap crystals in LiNbO3, or directly write surface waveguides or other guiding devices in the crystal. Ion beam-enhanced etching has been extensively applied for micro- or nanostructuring of LiNbO3 surfaces. Methods developed to fabricate a range of photonic guiding structures in LiNbO3 are introduced. Modifications of LiNbO3 through the use of various energetic ion beams, including changes in refractive index and properties related to the photonic guiding structures as well as to the materials (i.e., electro-optic, nonlinear optic, luminescent, and photorefractive features), are overviewed in detail. The application of these LiNbO3 photonic guiding structures in both micro- and nanophotonics are briefly summarized.

Triosmium Clusters on a Support: Determination of Structure by X-Ray Absorption Spectroscopy and High-Resolution Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shareghe, Mehraeen; Chi, Miaofang; Browning, Nigel D.

2011-01-01

The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X-ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration-corrected STEM. The samples were synthesized from [Os{sub 3}(CO){sub 12}] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high-angle annular dark-field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root-mean-square (rms) radii of 2.03 {+-} 0.06 {angstrom}. The EXAFS OsOs coordination number ofmore » 2.1 {+-} 0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02 {+-} 0.04 {angstrom}. The high-resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining OsOs distances of 2.80 {+-} 0.14 {angstrom}, matching the EXAFS value of 2.89 {+-} 0.06 {angstrom}. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters.« less

Physics Goals for the Planned Next Linear Collider Engineering Test Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raubenheimer, Tor O

2001-10-02

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Physics goals for the planned next linear collider engineering test facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Courtlandt L Bohn et al.

2001-06-26

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Physics goals for the planned next linear collider engineering test facility.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohn, C.; Michelotti, L.; Ostiguy, J.-F.

2001-07-17

The Next Linear Collider (NLC) Collaboration is planning to construct an Engineering Test Facility (ETF) at Fermilab. As presently envisioned, the ETF would comprise a fundamental unit of the NLC main linac to include X-band klystrons and modulators, a delay-line power-distribution system (DLDS), and NLC accelerating structures that serve as loads. The principal purpose of the ETF is to validate stable operation of the power-distribution system, first without beam, then with a beam having the NLC pulse structure. This paper concerns the possibility of configuring and using the ETF to accelerate beam with an NLC pulse structure, as well asmore » of doing experiments to measure beam-induced wakefields in the rf structures and their influence back on the beam.« less

Ion Beam Characterization of a NEXT Multi-Thruster Array Plume

NASA Technical Reports Server (NTRS)

Pencil, Eric J.; Foster, John E.; Patterson, Michael J.; Diaz, Esther M.; Van Noord, Jonathan L.; McEwen, Heather K.

2006-01-01

Three operational, engineering model, 7-kW ion thrusters and one instrumented, dormant thruster were installed in a cluster array in a large vacuum facility at NASA Glenn Research Center. A series of engineering demonstration tests were performed to evaluate the system performance impacts of operating various multiple-thruster configurations in an array. A suite of diagnostics was installed to investigate multiple-thruster operation impact on thruster performance and life, thermal interactions, and alternative system modes and architectures. The ion beam characterization included measuring ion current density profiles and ion energy distribution with Faraday probes and retarding potential analyzers, respectively. This report focuses on the ion beam characterization during single thruster operation, multiple thruster operation, various neutralizer configurations, and thruster gimbal articulation. Comparison of beam profiles collected during single and multiple thruster operation demonstrated the utility of superimposing single engine beam profiles to predict multi-thruster beam profiles. High energy ions were detected in the region 45 off the thruster axis, independent of thruster power, number of operating thrusters, and facility background pressure, which indicated that the most probable ion energy was not effected by multiple-thruster operation. There were no significant changes to the beam profiles collected during alternate thruster-neutralizer configurations, therefore supporting the viability of alternative system configuration options. Articulation of one thruster shifted its beam profile, whereas the beam profile of a stationary thruster nearby did not change, indicating there were no beam interactions which was consistent with the behavior of a collisionless beam expansion.

Structural properties and glass transition in Aln clusters

NASA Astrophysics Data System (ADS)

Sun, D. Y.; Gong, X. G.

1998-02-01

We have studied the structural and dynamical properties of several Aln clusters by the molecular-dynamics method combined with simulated annealing. The well-fitted glue potential is used to describe the interatomic interaction. The obtained atomic structures for n=13, 55, and 147 are in agreement with results from ab initio calculations. Our results have demonstrated that the disordered cluster Al43 can be considered as a glass cluster. The obtained thermal properties of glass cluster Al43 are clearly different from the results for high-symmetry clusters, its melting behavior has properties similar to those of a glass solid. The present studies also show that the surface melting behavior does not exist in the studied Aln clusters.

Structural and electronic properties Te62+ and Te82+: A DFT study

NASA Astrophysics Data System (ADS)

Sharma, Tamanna; Tamboli, Rohit; Kanhere, D. G.; Sharma, Raman

2018-05-01

Structural and electronic properties of Tellurium cluster (Ten) and their cations (Ten2+) (n = 6, 8) have been studied theoretically using VASP within generalized gradient approximation. Ground state geometries and higher energy isomers of these clusters have been examined on the basis of total free energy calculations. Lowest energy isomers of neutral clusters are ring like structures whereas the lowest energy isomers of cations are polyhedral cages. HOMO-LUMO gap in cationic clusters is small compared to its neutral clusters. Removal of two electrons from the neutral cluster raises the free energy. Analysis of free energy, HOMO-LUMO gap and density of states (DOS) show that neutral cluster are more stable than their cations.

Clustering Aspects in Nuclear Structure and Collisions

NASA Astrophysics Data System (ADS)

Horiuchi, H.

Four topics on nuclear clustering are discussed. The first subject is about the cluster formation in dilute matter which we think is now observed in heavy ion collisions at hundreds MeV/nucleon. The second subject is about our new proposal of the existense of alpha condensed states in light nuclei. Two other subjects are both about the clustering in neutron-rich nuclei. One is the cluster structures in neutron-rich Be and B isotopes. In these isotopes, the clustering prevails as fundamental characters of nuclear structure. The other is the report of our recent study about the possible relation of the clustering with the breaking of the neutron magic number N=20 in 32Mg and 30Ne.

Simulation of dynamics of beam structures with bolted joints using adjusted Iwan beam elements

NASA Astrophysics Data System (ADS)

Song, Y.; Hartwigsen, C. J.; McFarland, D. M.; Vakakis, A. F.; Bergman, L. A.

2004-05-01

Mechanical joints often affect structural response, causing localized non-linear stiffness and damping changes. As many structures are assemblies, incorporating the effects of joints is necessary to produce predictive finite element models. In this paper, we present an adjusted Iwan beam element (AIBE) for dynamic response analysis of beam structures containing joints. The adjusted Iwan model consists of a combination of springs and frictional sliders that exhibits non-linear behavior due to the stick-slip characteristic of the latter. The beam element developed is two-dimensional and consists of two adjusted Iwan models and maintains the usual complement of degrees of freedom: transverse displacement and rotation at each of the two nodes. The resulting element includes six parameters, which must be determined. To circumvent the difficulty arising from the non-linear nature of the inverse problem, a multi-layer feed-forward neural network (MLFF) is employed to extract joint parameters from measured structural acceleration responses. A parameter identification procedure is implemented on a beam structure with a bolted joint. In this procedure, acceleration responses at one location on the beam structure due to one known impulsive forcing function are simulated for sets of combinations of varying joint parameters. A MLFF is developed and trained using the patterns of envelope data corresponding to these acceleration histories. The joint parameters are identified through the trained MLFF applied to the measured acceleration response. Then, using the identified joint parameters, acceleration responses of the jointed beam due to a different impulsive forcing function are predicted. The validity of the identified joint parameters is assessed by comparing simulated acceleration responses with experimental measurements. The capability of the AIBE to capture the effects of bolted joints on the dynamic responses of beam structures, and the efficacy of the MLFF parameter identification procedure, are demonstrated.

Structures of small Pd Pt bimetallic clusters by Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Cheng, Daojian; Huang, Shiping; Wang, Wenchuan

2006-11-01

Segregation phenomena of Pd-Pt bimetallic clusters with icosahedral and decahedral structures are investigated by using Monte Carlo method based on the second-moment approximation of the tight-binding (TB-SMA) potentials. The simulation results indicate that the Pd atoms generally lie on the surface of the smaller clusters. The three-shell onion-like structures are observed in 55-atom Pd-Pt bimetallic clusters, in which a single Pd atom is located in the center, and the Pt atoms are in the middle shell, while the Pd atoms are enriched on the surface. With the increase of Pd mole fraction in 55-atom Pd-Pt bimetallic clusters, the Pd atoms occupy the vertices of clusters first, then edge and center sites, and finally the interior shell. It is noticed that some decahedral structures can be transformed into the icosahedron-like structure at 300 and 500 K. Comparisons are made with previous experiments and theoretical studies of Pd-Pt bimetallic clusters.

Fabrication of meso- and nano-scale structures on surfaces of chalcogenide semiconductors by surface hydrodynamic interference patterning

NASA Astrophysics Data System (ADS)

Bilanych, V.; Komanicky, V.; Lacková, M.; Feher, A.; Kuzma, V.; Rizak, V.

2015-10-01

We observe the change of surface relief on amorphous Ge-As-Se thin films after irradiation with an electron beam. The beam softens the glass and induces various topological surface changes in the irradiated area. The film relief change depends on the film thickness, deposited charge, and film composition. Various structures are formed: Gausian-like cones, extremely sharp Taylor cones, deep craters, and craters with large spires grown on the side. Our investigation shows that these effects can be at least partially a result of electro-hydrodynamic material flow, but the observed phenomena are likely more complex. When we irradiated structural patterns formed by the electron beam with a red laser beam, we could not only fully relax the produced patterns, but also form very complex and intricate superstructures. These organized meso- and nano-scale structures are formed by a combination of photo-induced structural relaxation, light interference on structures fabricated by the e-beam, and photo-induced material flow.

Anomalous small-angle scattering as a way to solve the Babinet principle problem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boiko, M. E., E-mail: m.e.boiko@mail.ioffe.ru; Sharkov, M. D.; Boiko, A. M.

2013-12-15

X-ray absorption spectra (XAS) have been used to determine the absorption edges of atoms present in a sample under study. A series of small-angle X-ray scattering (SAXS) measurements using different monochromatic X-ray beams at different wavelengths near the absorption edges is performed to solve the Babinet principle problem. The sizes of clusters containing atoms determined by the method of XAS were defined in SAXS experiments. In contrast to differential X-ray porosimetry, anomalous SAXS makes it possible to determine sizes of clusters of different atomic compositions.

Anomalous small-angle scattering as a way to solve the Babinet principle problem

NASA Astrophysics Data System (ADS)

Boiko, M. E.; Sharkov, M. D.; Boiko, A. M.; Bobyl, A. V.

2013-12-01

X-ray absorption spectra (XAS) have been used to determine the absorption edges of atoms present in a sample under study. A series of small-angle X-ray scattering (SAXS) measurements using different monochromatic X-ray beams at different wavelengths near the absorption edges is performed to solve the Babinet principle problem. The sizes of clusters containing atoms determined by the method of XAS were defined in SAXS experiments. In contrast to differential X-ray porosimetry, anomalous SAXS makes it possible to determine sizes of clusters of different atomic compositions.

Measuring the band structures of periodic beams using the wave superposition method

NASA Astrophysics Data System (ADS)

Junyi, L.; Ruffini, V.; Balint, D.

2016-11-01

Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in the dispersion curve measured from the experiments were deduced to be a result of a combination of measurement noise, the different placement of the accelerometer with finite mass, and the torsional mode.

High multiplicity α-particle breakup measurements to study α-condensate states

NASA Astrophysics Data System (ADS)

Bishop, J.; Kokalova, Tz; Freer, M.; Assie, M.; Acosta, L.; Bailey, S.; Cardella, G.; Curtis, N.; De Filippo, E.; Dell'Aquila, D.; De Luca, S.; Francalanza, L.; Gnoffo, B.; Lanzalone, G.; Lombardo, I.; Martorana, N.; Norella, S.; Pagano, A.; Pagano, E. V.; Papa, M.; Pirrone, S.; Politi, G.; Rizzo, F.; Russotto, P.; Quattrocchi, L.; Smith, R.; Stefan, I.; Trifirò, A.; Trimarchì, M.; Verde, G.; Vigilante, M.; Wheldon, C.

2017-06-01

An experiment was performed to investigate α-condensate states via high α-particle multiplicity breakup. The nucleus of interest was 28Si therefore to measure multiplicity 7 particle breakup events, a highly granular detector with a high solid angle coverage was required. For this purpose, the CHIMERA and FARCOS detectors at INFN LNS were employed. Particle identification was achieved through ΔE-E energy loss. The α-particle multiplicity was measured at three beam energies to investigate different excitation regimes in 28Si. At a beam energy where the energy is sufficient to provide the 7 α-particles with enough energy to be identified using the ΔE-E method, multiplicity 7 events can be seen. Given these high multiplicity events, the particles can be reconstructed to investigate the breakup of α-condensate states. Analysing the decay paths of these states can elucidate whether the state of interest corresponds to a non-cluster, clustered or condensed state.

Neutral and charged gallium clusters: structures, physical properties and implications for the melting features

NASA Astrophysics Data System (ADS)

Núñez, Sara; López, José M.; Aguado, Andrés

2012-09-01

We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims.We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims. Electronic supplementary information (ESI) available: Atomic coordinates (in xyz format and Å units) and point group symmetries for the global minimum structures reported in this paper. See DOI: 10.1039/c2nr31222k

Scaling effects in the impact response of graphite-epoxy composite beams

NASA Technical Reports Server (NTRS)

Jackson, Karen E.; Fasanella, Edwin L.

1989-01-01

In support of crashworthiness studies on composite airframes and substructure, an experimental and analytical study was conducted to characterize size effects in the large deflection response of scale model graphite-epoxy beams subjected to impact. Scale model beams of 1/2, 2/3, 3/4, 5/6, and full scale were constructed of four different laminate stacking sequences including unidirectional, angle ply, cross ply, and quasi-isotropic. The beam specimens were subjected to eccentric axial impact loads which were scaled to provide homologous beam responses. Comparisons of the load and strain time histories between the scale model beams and the prototype should verify the scale law and demonstrate the use of scale model testing for determining impact behavior of composite structures. The nonlinear structural analysis finite element program DYCAST (DYnamic Crash Analysis of STructures) was used to model the beam response. DYCAST analysis predictions of beam strain response are compared to experimental data and the results are presented.

Structural investigations in helium implanted cubic zirconia using grazing incidence XRD and EXAFS spectroscopy

NASA Astrophysics Data System (ADS)

Kuri, G.; Degueldre, C.; Bertsch, J.; Döbeli, M.

2010-06-01

The crystal structure and local atom arrangements surrounding Zr atoms were determined for a helium implanted cubic stabilized zirconia (CSZ) using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy, respectively, measured at glancing angles. The implanted specimen was prepared at a helium fluence of 2 × 10 16 cm -2 using He + beams at two energies (2.54 and 2.74 MeV) passing through a 8.0 μm Al absorber foil. XRD results identified the formation of a new rhombohedral phase in the helium embedded layer, attributed to internal stress as a result of expansion of the CSZ-lattice. Zr K-edge EXAFS data suggested loss of crystallinity in the implanted lattice and disorder of the Zr atoms environment. EXAFS Fourier transforms analysis showed that the average first-shell radius of the Zr sbnd O pair in the implanted sample was slightly larger than that of the CSZ standard. Common general disorder features were explained by rhombohedral type short-range ordered clusters. The average structural parameters estimated from the EXAFS data of unimplanted and implanted CSZ are compared and discussed. Potential of EXAFS as a local probe of atomic-scale structural modifications induced by helium implantation in CSZ is demonstrated.

Creating aperiodic photonic structures by synthesized Mathieu-Gauss beams

NASA Astrophysics Data System (ADS)

Vasiljević, Jadranka M.; Zannotti, Alessandro; Timotijević, Dejan V.; Denz, Cornelia; Savić, Dragana M. Jović

2017-08-01

We demonstrate a kind of aperiodic photonic structure realized using the interference of multiple Mathieu-Gauss beams. Depending on the beam configurations, their mutual distances, angles of rotation, or phase relations we are able to observe different classes of such aperiodic optically induced refractive index structures. Our experimental approach is based on the optical induction in a single parallel writing process.

A Geometric and Electrostatic Study of the [4Fe-4S] Cluster of Adenosine-5´-Phosphosulfate Reductase from Broken Symmetry Density Functional Calculations and Extended X-ray Absorption Fine Structure Spectroscopy

PubMed Central

Bhave, Devayani P.; Han, Wen-Ge; Pazicni, Samuel; Penner-Hahn, James E.; Carroll, Kate S.; Noodleman, Louis

2011-01-01

Adenosine-5’-phosphosulfate reductase (APSR) is an iron-sulfur protein that catalyses the reduction of adenosine-5’-phosphosulfate (APS) to sulfite. APSR coordinates to a [4Fe-4S] cluster via a conserved CC-X~80-CXXC motif and the cluster is essential for catalysis. Despite extensive functional, structural and spectroscopic studies, the exact role of the iron-sulfur cluster in APS reduction remains unknown. To gain an understanding into the role of the cluster, density functional theory (DFT) analysis and extended X-ray fine structure spectroscopy (EXAFS) have been performed to reveal insights into the coordination, geometry and electrostatics of the [4Fe-4S] cluster. XANES data confirms that the cluster is in the [4Fe-4S]2+ state in both native and substrate-bound APSR while EXAFS data recorded at ~0.1 Å resolution indicates that there is no significant change in the structure of the [4Fe-4S] cluster between the native and substrate-bound forms of the protein. On the other hand, DFT calculations provide an insight into the subtle differences between the geometry of the cluster in the native and APS-bound forms of APSR. A comparison between models with and without the tandem cysteine pair coordination of the cluster suggests a role for the unique coordination in facilitating a compact geometric structure and ‘fine-tuning’ the electronic structure to prevent reduction of the cluster. Further, calculations using models in which residue Lys144 is mutated to Ala confirm the finding that Lys144 serves as a crucial link in the interactions involving the [4Fe-4S] cluster and APS. PMID:21678934

Clusternomics: Integrative context-dependent clustering for heterogeneous datasets

PubMed Central

Wernisch, Lorenz

2017-01-01

Integrative clustering is used to identify groups of samples by jointly analysing multiple datasets describing the same set of biological samples, such as gene expression, copy number, methylation etc. Most existing algorithms for integrative clustering assume that there is a shared consistent set of clusters across all datasets, and most of the data samples follow this structure. However in practice, the structure across heterogeneous datasets can be more varied, with clusters being joined in some datasets and separated in others. In this paper, we present a probabilistic clustering method to identify groups across datasets that do not share the same cluster structure. The proposed algorithm, Clusternomics, identifies groups of samples that share their global behaviour across heterogeneous datasets. The algorithm models clusters on the level of individual datasets, while also extracting global structure that arises from the local cluster assignments. Clusters on both the local and the global level are modelled using a hierarchical Dirichlet mixture model to identify structure on both levels. We evaluated the model both on simulated and on real-world datasets. The simulated data exemplifies datasets with varying degrees of common structure. In such a setting Clusternomics outperforms existing algorithms for integrative and consensus clustering. In a real-world application, we used the algorithm for cancer subtyping, identifying subtypes of cancer from heterogeneous datasets. We applied the algorithm to TCGA breast cancer dataset, integrating gene expression, miRNA expression, DNA methylation and proteomics. The algorithm extracted clinically meaningful clusters with significantly different survival probabilities. We also evaluated the algorithm on lung and kidney cancer TCGA datasets with high dimensionality, again showing clinically significant results and scalability of the algorithm. PMID:29036190

Clusternomics: Integrative context-dependent clustering for heterogeneous datasets.

PubMed

Gabasova, Evelina; Reid, John; Wernisch, Lorenz

2017-10-01

Integrative clustering is used to identify groups of samples by jointly analysing multiple datasets describing the same set of biological samples, such as gene expression, copy number, methylation etc. Most existing algorithms for integrative clustering assume that there is a shared consistent set of clusters across all datasets, and most of the data samples follow this structure. However in practice, the structure across heterogeneous datasets can be more varied, with clusters being joined in some datasets and separated in others. In this paper, we present a probabilistic clustering method to identify groups across datasets that do not share the same cluster structure. The proposed algorithm, Clusternomics, identifies groups of samples that share their global behaviour across heterogeneous datasets. The algorithm models clusters on the level of individual datasets, while also extracting global structure that arises from the local cluster assignments. Clusters on both the local and the global level are modelled using a hierarchical Dirichlet mixture model to identify structure on both levels. We evaluated the model both on simulated and on real-world datasets. The simulated data exemplifies datasets with varying degrees of common structure. In such a setting Clusternomics outperforms existing algorithms for integrative and consensus clustering. In a real-world application, we used the algorithm for cancer subtyping, identifying subtypes of cancer from heterogeneous datasets. We applied the algorithm to TCGA breast cancer dataset, integrating gene expression, miRNA expression, DNA methylation and proteomics. The algorithm extracted clinically meaningful clusters with significantly different survival probabilities. We also evaluated the algorithm on lung and kidney cancer TCGA datasets with high dimensionality, again showing clinically significant results and scalability of the algorithm.

Manipulation of the micro and macro-structure of beams extracted from cyclotrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laxdal, R.E.

1995-09-01

It is standard practice in cyclotrons to alter the extracted micro-pulse width by using center-region slits and/or by chopping the beam before injection. The macro-structure can also be varied by means of pulsed or sinusoidal deflection devices before injection and/or after extraction. All above methods, however, involve cutting away the unwanted beam, thus reducing the time-averaged intensity. This paper will focus on some methods used to alter the time structure of extracted beams without significant beam loss. For example radial gradients in the accelerating fields from rf cavities can be utilized to compress, expand or even split longitudinally the circulatingmore » particle bunches. The macro-structure of the extracted beam can be altered by employing resonant extraction methods and replacing the static magnetic bump with either a pulsed or a sinusoidal transverse perturbation. The methods are most suitable for H cyclotrons but may also be considered in a limited scope for cyclotrons using direct extraction. Results of computer simulations and beam tests on the TRIUMF 500 MeV H{sup {minus}} cyclotron will be presented.« less

Photoionization mass spectrometry for the investigation of combustion generated nascent nanoparticles and their relation to laser induced incandescence

NASA Astrophysics Data System (ADS)

Grotheer, H.-H.; Wolf, K.; Hoffmann, K.

2011-08-01

Premixed laminar flat ethylene flames were investigated for nascent nanoparticles through photoionization mass spectrometry (PIMS). Using an atmospheric McKenna burner and ethylene air flames coupled to an atmospheric sampling system, within a relatively narrow C/O range two modes of these particles were found, which can be clearly distinguished with regard to their temperature dependence, their reactivity, and their ionization behaviour. Behind a diesel engine the same particles were observed. These results were corroborated using a low pressure ethylene-O2 flame coupled to a high resolution mass spectrometer. In this case, due to a special inlet system, it was possible to operate the flame in a fairly wide C/O range without clogging of the inlet nozzles. This allowed pursuing the development of particle size distribution functions (PSDF) well into the regime of mature soot. In addition, on the low mass side of the particle spectra measurements with unity resolution were possible and this allowed gaining information concerning their growth mechanism and structure. Finally, in an attempt to mimic Laser Induced Incandescence (LII) experiments the soot-laden molecular beam was exposed to IR irradiation. This resulted in a near complete destruction of nascent particles under LII typical fluences. Small C clusters between 3 and 17 C atoms were found. In addition and with much higher intensities, clusters comprising several hundreds of C atoms were also detected, the latter even at very low fluences when small clusters were totally absent.

Infrared Spectroscopy of Metal Ion Complexes: Models for Metal Ligand Interactions and Solvation

NASA Astrophysics Data System (ADS)

Duncan, Michael

2006-03-01

Weakly bound complexes of the form M^+-Lx (M=Fe, Ni, Co, etc.; L=CO2, C2H2, H2O, benzene, N2) are prepared in supersonic molecular beams by laser vaporization in a pulsed-nozzle cluster source. These species are mass analyzed and size-selected in a reflectron time-of-flight mass spectrometer. Clusters are photodissociated at infrared wavelengths with a Nd:YAG pumped infrared optical parametric oscillator/amplifier (OPO/OPA) laser or with a tunable infrared free-electron laser. M^+-(CO2)x complexes absorb near the free CO2 asymmetric stretch near 2349 cm-1 but with an interesting size dependent variation in the resonances. Small clusters have blue-shifted resonances, while larger complexes have additional bands due to surface CO2 molecules not attached to the metal. M^+(C2H2)n complexes absorb near the C-H stretches in acetylene, but resonances in metal complexes are red-shifted with repect to the isolated molecule. Ni^+ and Co^+ complexes with acetylene undergo intracluster cyclization reactions to form cyclobutadiene. Transition metal water complexes are studied in the O-H stretch region, and partial rotational structure can be measured. M^+(benzene) and M^+(benzene)2 ions (M=V, Ti, Al) represent half-sandwich and sandwich species, whose spectra are measured near the free benzene modes. These new IR spectra and their assignments will be discussed as well as other new IR spectra for similar complexes.

Lattice strain in irradiated materials unveils a prevalent defect evolution mechanism

NASA Astrophysics Data System (ADS)

Debelle, Aurélien; Crocombette, Jean-Paul; Boulle, Alexandre; Chartier, Alain; Jourdan, Thomas; Pellegrino, Stéphanie; Bachiller-Perea, Diana; Carpentier, Denise; Channagiri, Jayanth; Nguyen, Tien-Hien; Garrido, Frédérico; Thomé, Lionel

2018-01-01

Modification of materials using ion beams has become a widespread route to improve or design materials for advanced applications, from ion doping for microelectronic devices to emulation of nuclear reactor environments. Yet, despite decades of studies, major issues regarding ion/solid interactions are not solved, one of them being the lattice-strain development process in irradiated crystals. In this work, we address this question using a consistent approach that combines x-ray diffraction (XRD) measurements with both molecular dynamics (MD) and rate equation cluster dynamics (RECD) simulations. We investigate four distinct materials that differ notably in terms of crystalline structure and nature of the atomic bonding. We demonstrate that these materials exhibit a common behavior with respect to the strain development process. In fact, a strain build-up followed by a strain relaxation is observed in the four investigated cases. The strain variation is unambiguously ascribed to a change in the defect configuration, as revealed by MD simulations. Strain development is due to the clustering of interstitial defects into dislocation loops, while the strain release is associated with the disappearance of these loops through their integration into a network of dislocation lines. RECD calculations of strain depth profiles, which are in agreement with experimental data, indicate that the driving force for the change in the defect nature is the defect clustering process. This study paves the way for quantitative predictions of the microstructure changes in irradiated materials.

Combination of carbon ion beam and gemcitabine causes irreparable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo

PubMed Central

Sai, Sei; Wakai, Toshifumi; Vares, Guillaume; Yamada, Shigeru; Kamijo, Takehiko; Kamada, Tadashi; Shirai, Toshiyuki

2015-01-01

We try to elucidate whether a carbon ion beam alone or in combination with gemcitabine has advantages over X-ray in targeting putative pancreatic cancer stem-like cells (CSCs) in vitro and in vivo. Colony, spheroid formation and tumorigenicity assays confirmed that CD44+/ESA+ cells sorted from PANC1 and PK45 cells have more CSC properties than CD44−/ESA− cells. The number of colonies and spheroids formed from CSCs after carbon ion beam irradiation was significantly reduced compared to after X-ray irradiation, and they were extremely highly suppressed when carbon ion beam combined with gemcitabine. The relative biological effectiveness (RBE) values for the carbon ion beam relative to X-ray at the D10 levels for CSCs were 2.23-2.66. Expressions of multiple cell death-related genes were remarkably highly induced, and large numbers of γH2AX foci in CSCs were formed after carbon ion beam combined with gemcitabine. The highly expressed CSC markers were significantly inhibited after 30 Gy of carbon ion beam and almost lost after 25 Gy carbon ion beam combined with 50 mg/kg gemcitabine. In conclusion, a carbon ion beam combined with gemcitabine has superior potential to kill pancreatic CSCs via irreparable clustered DSB compared to a carbon ion alone or X-rays combined with gemcitabine. PMID:25849939

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

NASA Astrophysics Data System (ADS)

Dong, Hongying; Cao, Wanlin; Wu, Haipeng; Zhang, Jianwei; Xu, Fangfang

2013-12-01

A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Two-photon polymerization of a three dimensional structure using beams with orbital angular momentum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Shi-Jie; Li, Yan, E-mail: li@pku.edu.cn; Liu, Zhao-Pei

The focus of a beam with orbital angular momentum exhibits internal structure instead of an elliptical intensity distribution of a Gaussian beam, and the superposition of Gauss-Laguerre beams realized by two-dimensional phase modulation can generate a complex three-dimensional (3D) focus. By taking advantage of the flexibility of this 3D focus tailoring, we have fabricated a 3D microstructure with high resolution by two-photon polymerization with a single exposure. Furthermore, we have polymerized an array of double-helix structures that demonstrates optical chirality.

Stripline fast faraday cup for measuring GHz structure of ion beams

DOEpatents

Bogaty, John M.

1992-01-01

The Stripline Fast Faraday Cup is a device which is used to quantitatively and qualitatively measure gigahertz time structure characteristics of ion beams with energies up to at least 30 Mev per nucleon. A stripline geometry is employed in conjunction with an electrostatic screen and a Faraday cup to provide for analysis of the structural characteristics of an ion beam. The stripline geometry allows for a large reduction in the size of the instrument while the electrostatic screen permits measurements of the properties associated with low speed ion beams.

Crossover from disordered to core-shell structures of nano-oxide Y{sub 2}O{sub 3} dispersed particles in Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higgins, M. P.; Wang, L. M.; Gao, F., E-mail: gaofeium@umich.edu

Molecular dynamic simulations of Y{sub 2}O{sub 3} in bcc Fe and transmission electron microscopy (TEM) observations were used to understand the structure of Y{sub 2}O{sub 3} nano-clusters in an oxide dispersion strengthened steel matrix. The study showed that Y{sub 2}O{sub 3} nano-clusters below 2 nm were completely disordered. Y{sub 2}O{sub 3} nano-clusters above 2 nm, however, form a core-shell structure, with a shell thickness of 0.5–0.7 nm that is independent of nano-cluster size. Y{sub 2}O{sub 3} nano-clusters were surrounded by off-lattice Fe atoms, further increasing the stability of these nano-clusters. TEM was used to corroborate our simulation results and showed a crossover frommore » a disordered nano-cluster to a core-shell structure.« less

Spanish Dyslexic Spelling Abilities: The Case of Consonant Clusters

ERIC Educational Resources Information Center

Serrano, Francisca; Defior, Sylvia

2012-01-01

This paper investigates Spanish dyslexic spelling abilities: specifically, the influence of syllabic linguistic structure (simple vs consonant cluster) on children's spelling performance. Consonant clusters are phonologically complex structures, so it was anticipated that there would be lower spelling performance for these syllabic structures than…

BEAM web server: a tool for structural RNA motif discovery.

PubMed

Pietrosanto, Marco; Adinolfi, Marta; Casula, Riccardo; Ausiello, Gabriele; Ferrè, Fabrizio; Helmer-Citterich, Manuela

2018-03-15

RNA structural motif finding is a relevant problem that becomes computationally hard when working on high-throughput data (e.g. eCLIP, PAR-CLIP), often represented by thousands of RNA molecules. Currently, the BEAM server is the only web tool capable to handle tens of thousands of RNA in input with a motif discovery procedure that is only limited by the current secondary structure prediction accuracies. The recently developed method BEAM (BEAr Motifs finder) can analyze tens of thousands of RNA molecules and identify RNA secondary structure motifs associated to a measure of their statistical significance. BEAM is extremely fast thanks to the BEAR encoding that transforms each RNA secondary structure in a string of characters. BEAM also exploits the evolutionary knowledge contained in a substitution matrix of secondary structure elements, extracted from the RFAM database of families of homologous RNAs. The BEAM web server has been designed to streamline data pre-processing by automatically handling folding and encoding of RNA sequences, giving users a choice for the preferred folding program. The server provides an intuitive and informative results page with the list of secondary structure motifs identified, the logo of each motif, its significance, graphic representation and information about its position in the RNA molecules sharing it. The web server is freely available at http://beam.uniroma2.it/ and it is implemented in NodeJS and Python with all major browsers supported. marco.pietrosanto@uniroma2.it. Supplementary data are available at Bioinformatics online.

Beam wander and M2-factor of partially coherent electromagnetic hollow Gaussian beam propagating through non-Kolmogorov turbulence

NASA Astrophysics Data System (ADS)

Xu, Yonggen; Tian, Huanhuan; Dan, Youquan; Feng, Hao; Wang, Shijian

2017-04-01

Propagation formulae for M2-factor and beam wander of partially coherent electromagnetic hollow Gaussian (PCEHG) beam in non-Kolmogorov turbulence are derived based on the extended Huygens-Fresnel principle and the second-order moments of the Wigner distribution function. Our results indicate that the normalized M2-factors of PCEHG beam with larger beam order, waist width, inner scale of turbulence, the generalized exponent parameter, and smaller transverse coherent widths, outer scale of turbulence, the generalized structure parameter are less affected by the turbulence. The root mean square beam wander and relative beam wander are more obvious for PCEHG beam with smaller beam order, larger inner and outer scales of turbulence, exponent parameter, transverse coherent widths, and the generalized structure parameter. What is more, the beam wander properties of PCEHG beam in non-Kolmogorov turbulence are very different from M2-factor and spreading properties of beam in turbulence.

Ground and satellite observations of multiple sun-aligned auroral arcs on the duskside

NASA Astrophysics Data System (ADS)

Hosokawa, K.; Maggiolo, R.; Zhang, Y.; Fear, R. C.; Fontaine, D.; Cumnock, J. A.; Kullen, A.; Milan, S. E.; Kozlovsky, A.; Echim, M.; Shiokawa, K.

2014-12-01

Sun-aligned auroral arcs (SAAs) are one of the outstanding phenomena in the high-latitude region during periods of northward interplanetary magnetic field (IMF). Smaller scale SAAs tend to occur either in the duskside or dawnside of the polar cap and are known to drift in the dawn-dusk direction depending on the sign of the IMF By. Studies of SAAs are of particular importance because they represent dynamical characteristics of their source plasma in the magnetosphere, for example in the interaction region between the solar wind and magnetosphere or in the boundary between the plasma sheet and tail lobe. To date, however, very little has been known about the spatial structure and/or temporal evolution of the magnetospheric counterpart of SAAs. In order to gain more comprehensive understanding of the field-aligned plasma transport in the vicinity of SAAs, we have investigated an event of SAAs on November 10, 2005, during which multiple SAAs were detected by a ground-based all-sky camera at Resolute Bay, Canada. During this interval, several SAAs were detached from the duskside oval and moved poleward. The large-scale structure of these arcs was visualized by space-based imagers of TIMED/GUVI and DMSP/SSUSI. In addition to these optical observations, we employ the Cluster satellites to reveal the high-altitude particle signature corresponding to the small-scale SAAs. The ionospheric footprints of the 4 Cluster satellites encountered the SAAs sequentially and observed well correlated enhancements of electron fluxes at weak energies (< 1 keV). The Cluster satellites also detected signatures of upflowing beams of ions and electrons in the vicinity of the SAAs. This implies that these ions and electrons were accelerated upward by a quasi-stationary electric field existing in the vicinity of the SAAs and constitute a current system in the magnetosphere-ionosphere coupling system. Ionospheric convection measurement from one of the SuperDARN radars shows an indication that the SAAs are embedded in the lobe cell during northward IMF conditions. In the presentation, we will show the results of detailed comparison between the ground-based radio and optical signatures of the SAAs and those obtained by the Cluster spacecraft at magnetospheric altitudes.

Far-infrared image restoration analysis of the protostellar cluster in S140

NASA Technical Reports Server (NTRS)

Lester, D. F.; Harvey, P. M.; Joy, M.; Ellis, H. B., Jr.

1986-01-01

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented.

Smoothing metallic glasses without introducing crystallization by gas cluster ion beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Lin; Chen, Di; Myers, Michael

2013-03-11

We show that 30 keV Ar cluster ion bombardment of Ni{sub 52.5}Nb{sub 10}Zr{sub 15}Ti{sub 15}Pt{sub 7.5} metallic glass (MG) can remove surface mountain-like features and reduce the root mean square surface roughness from 12 nm to 0.7 nm. X-ray diffraction analysis reveals no crystallization after cluster ion irradiation. Molecular dynamics simulations show that, although damage cascades lead to local melting, the subsequent quenching rate is a few orders of magnitude higher than the critical cooling rate for MG formation, thus the melted zone retains its amorphous nature down to room temperature. These findings can be applied to obtain ultra-smooth MGsmore » without introducing crystallization.« less

Interactions of small platinum clusters with the TiC(001) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Jianjun; Li, Shasha; Chu, Xingli

2015-11-14

Density functional theory calculations are used to elucidate the interactions of small platinum clusters (Pt{sub n}, n = 1–5) with the TiC(001) surface. The results are analyzed in terms of geometric, energetic, and electronic properties. It is found that a single Pt atom prefers to be adsorbed at the C-top site, while a Pt{sub 2} cluster prefers dimerization and a Pt{sub 3} cluster forms a linear structure on the TiC(001). As for the Pt{sub 4} cluster, the three-dimensional distorted tetrahedral structure and the two-dimensional square structure almost have equal stability. In contrast with the two-dimensional isolated Pt{sub 5} cluster, the adsorbed Pt{submore » 5} cluster prefers a three-dimensional structure on TiC(001). Substantial charge transfer takes place from TiC(001) surface to the adsorbed Pt{sub n} clusters, resulting in the negatively charged Pt{sub n} clusters. At last, the d-band centers of the absorbed Pt atoms and their implications in the catalytic activity are discussed.« less

Optimizing weak lensing mass estimates for cluster profile uncertainty

DOE PAGES

Gruen, D.; Bernstein, G. M.; Lam, T. Y.; ...

2011-09-11

Weak lensing measurements of cluster masses are necessary for calibrating mass-observable relations (MORs) to investigate the growth of structure and the properties of dark energy. However, the measured cluster shear signal varies at fixed mass M 200m due to inherent ellipticity of background galaxies, intervening structures along the line of sight, and variations in the cluster structure due to scatter in concentrations, asphericity and substructure. We use N-body simulated halos to derive and evaluate a weak lensing circular aperture mass measurement M ap that minimizes the mass estimate variance <(M ap - M 200m) 2> in the presence of allmore » these forms of variability. Depending on halo mass and observational conditions, the resulting mass estimator improves on M ap filters optimized for circular NFW-profile clusters in the presence of uncorrelated large scale structure (LSS) about as much as the latter improve on an estimator that only minimizes the influence of shape noise. Optimizing for uncorrelated LSS while ignoring the variation of internal cluster structure puts too much weight on the profile near the cores of halos, and under some circumstances can even be worse than not accounting for LSS at all. As a result, we discuss the impact of variability in cluster structure and correlated structures on the design and performance of weak lensing surveys intended to calibrate cluster MORs.« less

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, John R.

1986-01-01

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

Electron beam enhanced surface modification for making highly resolved structures

DOEpatents

Pitts, J.R.

1984-10-10

A method for forming high resolution submicron structures on a substrate is provided by direct writing with a submicron electron beam in a partial pressure of a selected gas phase characterized by the ability to dissociate under the beam into a stable gaseous leaving group and a reactant fragment that combines with the substrate material under beam energy to form at least a surface compound. Variations of the method provide semiconductor device regions on doped silicon substrates, interconnect lines between active sites, three dimensional electronic chip structures, electron beam and optical read mass storage devices that may include color differentiated data areas, and resist areas for use with selective etching techniques.

Space fabrication demonstration system, technical volume

NASA Technical Reports Server (NTRS)

1979-01-01

The automatic beam builder ABB was developed, fabricated, and demonstrated within the established contract cost and schedule constraints. The ABB demonstrated the feasibility of: producing lightweight beams automatically within the required rate of 1 to 5 ft of completed beam per minute and producing structurally sound beams with axial design load of 5538 N based on the Grumman photovoltaic satellite solar power system design reference structure.

Symplectic modeling of beam loading in electromagnetic cavities

DOE PAGES

Abell, Dan T.; Cook, Nathan M.; Webb, Stephen D.

2017-05-22

Simulating beam loading in radio frequency accelerating structures is critical for understanding higher-order mode effects on beam dynamics, such as beam break-up instability in energy recovery linacs. Full wave simulations of beam loading in radio frequency structures are computationally expensive, and while reduced models can ignore essential physics, it can be difficult to generalize. Here, we present a self-consistent algorithm derived from the least-action principle which can model an arbitrary number of cavity eigenmodes and with a generic beam distribution. It has been implemented in our new Open Library for Investigating Vacuum Electronics (OLIVE).

Density functional study of structural and electronic properties of bimetallic silver-gold clusters: Comparison with pure gold and silver clusters

NASA Astrophysics Data System (ADS)

Bonacic-Koutecky, Vlasta; Burda, Jaroslav; Mitric, Roland; Ge, Maofa; Zampella, Giuseppe; Fantucci, Piercarlo

2002-08-01

Bimetallic silver-gold clusters offer an excellent opportunity to study changes in metallic versus "ionic" properties involving charge transfer as a function of the size and the composition, particularly when compared to pure silver and gold clusters. We have determined structures, ionization potentials, and vertical detachment energies for neutral and charged bimetallic AgmAun 3[less-than-or-equal](m+n)[less-than-or-equal]5 clusters. Calculated VDE values compare well with available experimental data. In the stable structures of these clusters Au atoms assume positions which favor the charge transfer from Ag atoms. Heteronuclear bonding is usually preferred to homonuclear bonding in clusters with equal numbers of hetero atoms. In fact, stable structures of neutral Ag2Au2, Ag3Au3, and Ag4Au4 clusters are characterized by the maximum number of hetero bonds and peripheral positions of Au atoms. Bimetallic tetramer as well as hexamer are planar and have common structural properties with corresponding one-component systems, while Ag4Au4 and Ag8 have 3D forms in contrast to Au8 which assumes planar structure. At the density functional level of theory we have shown that this is due to participation of d electrons in bonding of pure Aun clusters while s electrons dominate bonding in pure Agm as well as in bimetallic clusters. In fact, Aun clusters remain planar for larger sizes than Agm and AgnAun clusters. Segregation between two components in bimetallic systems is not favorable, as shown in the example of Ag5Au5 cluster. We have found that the structures of bimetallic clusters with 20 atoms Ag10Au10 and Ag12Au8 are characterized by negatively charged Au subunits embedded in Ag environment. In the latter case, the shape of Au8 is related to a pentagonal bipyramid capped by one atom and contains three exposed negatively charged Au atoms. They might be suitable for activating reactions relevant to catalysis. According to our findings the charge transfer in bimetallic clusters is responsible for formation of negatively charged gold subunits which are expected to be reactive, a situation similar to that of gold clusters supported on metal oxides.

Structure of overheated metal clusters: MD simulation study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vorontsov, Alexander

2015-08-17

The structure of overheated metal clusters appeared in condensation process was studied by computer simulation techniques. It was found that clusters with size larger than several tens of atoms have three layers: core part, intermediate dense packing layer and a gas- like shell with low density. The change of the size and structure of these layers with the variation of internal energy and the size of cluster is discussed.

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pohlit, Merlin, E-mail: pohlit@physik.uni-frankfurt.de; Porrati, Fabrizio; Huth, Michael

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamicsmore » of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.« less

An Analysis of Rich Cluster Redshift Survey Data for Large Scale Structure Studies

NASA Astrophysics Data System (ADS)

Slinglend, K.; Batuski, D.; Haase, S.; Hill, J.

1994-12-01

The results from the COBE satellite show the existence of structure on scales on the order of 10% or more of the horizon scale of the universe. Rich clusters of galaxies from Abell's catalog show evidence of structure on scales of 100 Mpc and may hold the promise of confirming structure on the scale of the COBE result. However, many Abell clusters have zero or only one measured redshift, so present knowledge of their three dimensional distribution has quite large uncertainties. The shortage of measured redshifts for these clusters may also mask a problem of projection effects corrupting the membership counts for the clusters. Our approach in this effort has been to use the MX multifiber spectrometer on the Steward 2.3m to measure redshifts of at least ten galaxies in each of 80 Abell cluster fields with richness class R>= 1 and mag10 <= 16.8 (estimated z<= 0.12) and zero or one measured redshifts. This work will result in a deeper, more complete (and reliable) sample of positions of rich clusters. Our primary intent for the sample is for two-point correlation and other studies of the large scale structure traced by these clusters in an effort to constrain theoretical models for structure formation. We are also obtaining enough redshifts per cluster so that a much better sample of reliable cluster velocity dispersions will be available for other studies of cluster properties. To date, we have collected such data for 64 clusters, and for most of them, we have seven or more cluster members with redshifts, allowing for reliable velocity dispersion calculations. Velocity histograms and stripe density plots for several interesting cluster fields are presented, along with summary tables of cluster redshift results. Also, with 10 or more redshifts in most of our cluster fields (30({') } square, just about an `Abell diameter' at z ~ 0.1) we have investigated the extent of projection effects within the Abell catalog in an effort to quantify and understand how this may effect the Abell sample.

Studies of the Virgo cluster. VI - Morphological and kinematical structure of the Virgo cluster

NASA Technical Reports Server (NTRS)

Binggeli, Bruno; Tammann, G. A.; Sandage, Allan

1987-01-01

The structure of the Virgo cluster is analyzed on the basis of the positions, Hubble types, and radial velocities of 1277 Virgo cluster galaxies. The surface distribution of galaxies is considered according to type, and is discussed using maps, isopleths, strip counts, and radial-density distributions. It is found that the Virgo cluster shows pronounced double structure. The main concentration has a large velocity dispersion and is made up predominantly of early-type galaxies, while the secondary concentration has a much smaller velocity dispersion and contains late types. There is a strong spatial segregation of the Hubble types, the early-type galaxies being more concentrated toward the cluster center. There is significant substructure in the cluster core. The irregularity of the Virgo cluster in both configuration and velocity space shows that the core and the envelope are still forming, and hence that the cluster is young.

Information Theory and Voting Based Consensus Clustering for Combining Multiple Clusterings of Chemical Structures.

PubMed

Saeed, Faisal; Salim, Naomie; Abdo, Ammar

2013-07-01

Many consensus clustering methods have been applied in different areas such as pattern recognition, machine learning, information theory and bioinformatics. However, few methods have been used for chemical compounds clustering. In this paper, an information theory and voting based algorithm (Adaptive Cumulative Voting-based Aggregation Algorithm A-CVAA) was examined for combining multiple clusterings of chemical structures. The effectiveness of clusterings was evaluated based on the ability of the clustering method to separate active from inactive molecules in each cluster, and the results were compared with Ward's method. The chemical dataset MDL Drug Data Report (MDDR) and the Maximum Unbiased Validation (MUV) dataset were used. Experiments suggest that the adaptive cumulative voting-based consensus method can improve the effectiveness of combining multiple clusterings of chemical structures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laser beam generating apparatus

DOEpatents

Warner, Bruce E.; Duncan, David B.

1993-01-01

Laser beam generating apparatus including a septum segment disposed longitudinally within the tubular structure of the apparatus. The septum provides for radiatively dissipating heat buildup within the tubular structure and for generating relatively uniform laser beam pulses so as to minimize or eliminate radial pulse delays (the chevron effect).

Laser beam generating apparatus

DOEpatents

Warner, Bruce E.; Duncan, David B.

1994-01-01

Laser beam generating apparatus including a septum segment disposed longitudinally within the tubular structure of the apparatus. The septum provides for radiatively dissipating heat buildup within the tubular structure and for generating relatively uniform laser beam pulses so as to minimize or eliminate radial pulse delays (the chevron effect).

Application of a parallel genetic algorithm to the global optimization of medium-sized Au-Pd sub-nanometre clusters

NASA Astrophysics Data System (ADS)

Hussein, Heider A.; Demiroglu, Ilker; Johnston, Roy L.

2018-02-01

To contribute to the discussion of the high activity and reactivity of Au-Pd system, we have adopted the BPGA-DFT approach to study the structural and energetic properties of medium-sized Au-Pd sub-nanometre clusters with 11-18 atoms. We have examined the structural behaviour and stability as a function of cluster size and composition. The study suggests 2D-3D crossover points for pure Au clusters at 14 and 16 atoms, whereas pure Pd clusters are all found to be 3D. For Au-Pd nanoalloys, the role of cluster size and the influence of doping were found to be extensive and non-monotonic in altering cluster structures. Various stability criteria (e.g. binding energies, second differences in energy, and mixing energies) are used to evaluate the energetics, structures, and tendency of segregation in sub-nanometre Au-Pd clusters. HOMO-LUMO gaps were calculated to give additional information on cluster stability and a systematic homotop search was used to evaluate the energies of the generated global minima of mono-substituted clusters and the preferred doping sites, as well as confirming the validity of the BPGA-DFT approach.

Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure.

PubMed

Zhang, Yaxin; Zhou, Yucong; Gang, Yin; Jiang, Guili; Yang, Ziqiang

2017-01-23

Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation.

Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure

PubMed Central

Zhang, Yaxin; Zhou, Yucong; Gang, Yin; Jiang, Guili; Yang, Ziqiang

2017-01-01

Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation. PMID:28112234

The influence of air-filled structures on wave propagation and beam formation of a pygmy sperm whale (Kogia breviceps) in horizontal and vertical planes.

PubMed

Song, Zhongchang; Zhang, Yu; Thornton, Steven W; Li, Songhai; Dong, Jianchen

2017-10-01

The wave propagation, sound field, and transmission beam pattern of a pygmy sperm whale (Kogia breviceps) were investigated in both the horizontal and vertical planes. Results suggested that the signals obtained at both planes were similarly characterized with a high peak frequency and a relatively narrow bandwidth, close to the ones recorded from live animals. The sound beam measured outside the head in the vertical plane was narrower than that of the horizontal one. Cases with different combinations of air-filled structures in both planes were used to study the respective roles in controlling wave propagation and beam formation. The wave propagations and beam patterns in the horizontal and vertical planes elucidated the important reflection effect of the spermaceti and vocal chambers on sound waves, which was highly significant in forming intensive forward sound beams. The air-filled structures, the forehead soft tissues and skull structures formed wave guides in these two planes for emitted sounds to propagate forward.

Low-temperature cluster catalysis.

PubMed

Judai, Ken; Abbet, Stéphane; Wörz, Anke S; Heiz, Ulrich; Henry, Claude R

2004-03-10

Free and supported metal clusters reveal unique chemical and physical properties, which vary as a function of size as each cluster possesses a characteristic electron confinement. Several previous experimental results showed that the outcome of a given chemical reaction can be controlled by tuning the cluster size. However, none of the examples indicate that clusters prepared in the gas phase and then deposited on a support material are indeed catalytically active over several reaction cycles nor that their catalytic properties remain constant during such a catalytic process. In this work we report turn-over frequencies (TOF) for Pd(n) (n = 4, 8, 30) clusters using pulsed molecular beam experiments. The obtained results illustrate that the catalytic reactivity for the NO reduction by CO (CO + NO --> 1/2N(2) + CO(2)) is indeed a function of cluster size and that the measured TOF remain constant at a given temperature. More interestingly, the temperature of maximal reactivity is at least 100 K lower than observed for palladium nanoparticles or single crystals. One reason for this surprising observation is the character of the binding sites of these small clusters: N(2) forms already at relatively low temperatures (400 and 450 K) and therefore poisoning by adsorbed nitrogen adatoms is prevented. Thus, small clusters not only open the possibility of tuning a catalytic process by changing cluster size, but also of catalyzing chemical reactions at low temperatures.

Efficiency Improvements to the Displacement Based Multilevel Structural Optimization Algorithm

NASA Technical Reports Server (NTRS)

Plunkett, C. L.; Striz, A. G.; Sobieszczanski-Sobieski, J.

2001-01-01

Multilevel Structural Optimization (MSO) continues to be an area of research interest in engineering optimization. In the present project, the weight optimization of beams and trusses using Displacement based Multilevel Structural Optimization (DMSO), a member of the MSO set of methodologies, is investigated. In the DMSO approach, the optimization task is subdivided into a single system and multiple subsystems level optimizations. The system level optimization minimizes the load unbalance resulting from the use of displacement functions to approximate the structural displacements. The function coefficients are then the design variables. Alternately, the system level optimization can be solved using the displacements themselves as design variables, as was shown in previous research. Both approaches ensure that the calculated loads match the applied loads. In the subsystems level, the weight of the structure is minimized using the element dimensions as design variables. The approach is expected to be very efficient for large structures, since parallel computing can be utilized in the different levels of the problem. In this paper, the method is applied to a one-dimensional beam and a large three-dimensional truss. The beam was tested to study possible simplifications to the system level optimization. In previous research, polynomials were used to approximate the global nodal displacements. The number of coefficients of the polynomials equally matched the number of degrees of freedom of the problem. Here it was desired to see if it is possible to only match a subset of the degrees of freedom in the system level. This would lead to a simplification of the system level, with a resulting increase in overall efficiency. However, the methods tested for this type of system level simplification did not yield positive results. The large truss was utilized to test further improvements in the efficiency of DMSO. In previous work, parallel processing was applied to the subsystems level, where the derivative verification feature of the optimizer NPSOL had been utilized in the optimizations. This resulted in large runtimes. In this paper, the optimizations were repeated without using the derivative verification, and the results are compared to those from the previous work. Also, the optimizations were run on both, a network of SUN workstations using the MPICH implementation of the Message Passing Interface (MPI) and on the faster Beowulf cluster at ICASE, NASA Langley Research Center, using the LAM implementation of UP]. The results on both systems were consistent and showed that it is not necessary to verify the derivatives and that this gives a large increase in efficiency of the DMSO algorithm.

Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations

PubMed Central

Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun

2016-01-01

We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters. PMID:27439955

Dynamics of laser-driven proton beam focusing and transport into solid density matter

NASA Astrophysics Data System (ADS)

Kim, J.; McGuffey, C.; Beg, F.; Wei, M.; Mariscal, D.; Chen, S.; Fuchs, J.

2016-10-01

Isochoric heating and local energy deposition capabilities make intense proton beams appealing for studying high energy density physics and the Fast Ignition of inertial confinement fusion. To study proton beam focusing that results in high beam density, experiments have been conducted using different target geometries irradiated by a kilojoule, 10 ps pulse of the OMEGA EP laser. The beam focus was measured by imaging beam-induced Cu K-alpha emission on a Cu foil that was positioned at a fixed distance. Compared to a free target, structured targets having shapes of wedge and cone show a brighter and narrower K-alpha radiation emission spot on a Cu foil indicating higher beam focusability. Experimentally observed images with proton radiography demonstrate the existence of transverse fields on the structures. Full-scale simulations including the contribution of a long pulse duration of the laser confirm that such fields can be caused by hot electrons moving through the structures. The simulated fields are strong enough to reflect the diverging main proton beam and pinch a transverse probe beam. Detailed simulation results including the beam focusing and transport of the focused intense proton beam in Cu foil will be presented. This work was supported by the National Laser User Facility Program through Award DE-NA0002034.

The Evolution of Globular Cluster Systems In Early-Type Galaxies

NASA Astrophysics Data System (ADS)

Grillmair, Carl

1999-07-01

We will measure structural parameters {core radii and concentrations} of globular clusters in three early-type galaxies using deep, four-point dithered observations. We have chosen globular cluster systems which have young, medium-age and old cluster populations, as indicated by cluster colors and luminosities. Our primary goal is to test the hypothesis that globular cluster luminosity functions evolve towards a ``universal'' form. Previous observations have shown that young cluster systems have exponential luminosity functions rather than the characteristic log-normal luminosity function of old cluster systems. We will test to see whether such young system exhibits a wider range of structural parameters than an old systems, and whether and at what rate plausible disruption mechanisms will cause the luminosity function to evolve towards a log-normal form. A simple observational comparison of structural parameters between different age cluster populations and between diff er ent sub-populations within the same galaxy will also provide clues concerning both the formation and destruction mechanisms of star clusters, the distinction between open and globular clusters, and the advisability of using globular cluster luminosity functions as distance indicators.

GaN-based light emitting diodes using p-type trench structure for improving internal quantum efficiency

NASA Astrophysics Data System (ADS)

Kim, Garam; Sun, Min-Chul; Kim, Jang Hyun; Park, Euyhwan; Park, Byung-Gook

2017-01-01

In order to improve the internal quantum efficiency of GaN-based LEDs, a LED structure featuring a p-type trench in the multi-quantum well (MQW) is proposed. This structure has effects on spreading holes into the MQW and reducing the quantum-confined stark effect (QCSE). In addition, two simple fabrication methods using electron-beam (e-beam) lithography or selective wet etching for manufacturing the p-type structure are also proposed. From the measurement results of the manufactured GaN-based LEDs, it is confirmed that the proposed structure using e-beam lithography or selective wet etching shows improved light output power compared to the conventional structure because of more uniform hole distribution. It is also confirmed that the proposed structure formed by e-beam lithography has a significant effect on strain relaxation and reduction in the QCSE from the electro-luminescence measurement.

Radiation damage and thermal shock response of carbon-fiber-reinforced materials to intense high-energy proton beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simos, N.; Zhong, Z.; Ghose, S.

Here, a comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have beenmore » studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences ≥5×10 20 p/cm 2. The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiber-reinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation load-displacement behavior even after low dose levels (~5×10 18 p cm -2). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence ~5×10 20 p cm -2. Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the “as-received” 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the c axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.« less

Radiation damage and thermal shock response of carbon-fiber-reinforced materials to intense high-energy proton beams

DOE PAGES

Simos, N.; Zhong, Z.; Ghose, S.; ...

2016-11-16

Here, a comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have beenmore » studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences ≥5×10 20 p/cm 2. The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiber-reinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation load-displacement behavior even after low dose levels (~5×10 18 p cm -2). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence ~5×10 20 p cm -2. Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the “as-received” 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the c axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.« less

Radiation damage and thermal shock response of carbon-fiber-reinforced materials to intense high-energy proton beams

NASA Astrophysics Data System (ADS)

Simos, N.; Zhong, Z.; Ghose, S.; Kirk, H. G.; Trung, L.-P.; McDonald, K. T.; Kotsina, Z.; Nocera, P.; Assmann, R.; Redaelli, S.; Bertarelli, A.; Quaranta, E.; Rossi, A.; Zwaska, R.; Ammigan, K.; Hurh, P.; Mokhov, N.

2016-11-01

A comprehensive study on the effects of energetic protons on carbon-fiber composites and compounds under consideration for use as low-Z pion production targets in future high-power accelerators and low-impedance collimating elements for intercepting TeV-level protons at the Large Hadron Collider has been undertaken addressing two key areas, namely, thermal shock absorption and resistance to irradiation damage. Carbon-fiber composites of various fiber weaves have been widely used in aerospace industries due to their unique combination of high temperature stability, low density, and high strength. The performance of carbon-carbon composites and compounds under intense proton beams and long-term irradiation have been studied in a series of experiments and compared with the performance of graphite. The 24-GeV proton beam experiments confirmed the inherent ability of a 3D C/C fiber composite to withstand a thermal shock. A series of irradiation damage campaigns explored the response of different C/C structures as a function of the proton fluence and irradiating environment. Radiolytic oxidation resulting from the interaction of oxygen molecules, the result of beam-induced radiolysis encountered during some of the irradiation campaigns, with carbon atoms during irradiation with the presence of a water coolant emerged as a dominant contributor to the observed structural integrity loss at proton fluences ≥5 ×1020 p /cm2 . The carbon-fiber composites were shown to exhibit significant anisotropy in their dimensional stability driven by the fiber weave and the microstructural behavior of the fiber and carbon matrix accompanied by the presence of manufacturing porosity and defects. Carbon-fiber-reinforced molybdenum-graphite compounds (MoGRCF) selected for their impedance properties in the Large Hadron Collider beam collimation exhibited significant decrease in postirradiation load-displacement behavior even after low dose levels (˜5 ×1018 p cm-2 ). In addition, the studied MoGRCF compound grade suffered a high degree of structural degradation while being irradiated in a vacuum after a fluence ˜5 ×1020 p cm-2 . Finally, x-ray diffraction studies on irradiated C/C composites and a carbon-fiber-reinforced Mo-graphite compound revealed (a) low graphitization in the "as-received" 3D C/C and high graphitization in the MoGRCF compound, (b) irradiation-induced graphitization of the least crystallized phases in the carbon fibers of the 2D and 3D C/C composites, (c) increased interplanar distances along the c axis of the graphite crystal with increasing fluence, and (d) coalescence of interstitial clusters after irradiation forming new crystalline planes between basal planes and excellent agreement with fast neutron irradiation effects.

Flow over gravel beds with clusters

NASA Astrophysics Data System (ADS)

Little, M.; Venditti, J. G.

2014-12-01

The structure of a gravel bed has been shown to alter the entrainment threshold. Structures such as clusters, reticulate stone cells and other discrete structures lock grains together, making it more difficult for them to be mobilized. These structures also generate form drag, reducing the shear stress available for mobilization. Form drag over gravel beds is often assumed to be negligible, but this assumption is not well supported. Here, we explore how cluster density and arrangement affect flow resistance and the flow structure over a fixed gravel bed in a flume experiment. Cluster density was varied from 6 to 68.3 clusters per square meter which corresponds to areal bed coverages of 2 to 17%. We used regular, irregular and random arrangements of the clusters. Our results show that flow resistance over a planar gravel bed initially declines, then increases with flow depth. The addition of clusters increases flow resistance, but the effect is dependent on cluster density, flow depth and arrangement. At the highest density, clusters can increase flow resistance as by as much as 8 times when compared to flat planar bed with no grain-related form drag. Spatially resolved observations of flow over the clusters indicate that a well-defined wake forms in the lee of each cluster. At low cluster density, the wakes are isolated and weak. As cluster density increases, the wakes become stronger. At the highest density, the wakes interact and the within cluster flow field detaches from the overlying flow. This generates a distinct shear layer at the height of the clusters. In spite of this change in the flow field at high density, our results suggest that flow resistance simply increases with cluster density. Our results suggest that the form drag associated with a gravel bed can be substantial and that it depends on the arrangement of the grains on the bed.

Silicon-germanium and platinum silicide nanostructures for silicon based photonics

NASA Astrophysics Data System (ADS)

Storozhevykh, M. S.; Dubkov, V. P.; Arapkina, L. V.; Chizh, K. V.; Mironov, S. A.; Chapnin, V. A.; Yuryev, V. A.

2017-05-01

This paper reports a study of two types of silicon based nanostructures prospective for applications in photonics. The first ones are Ge/Si(001) structures forming at room temperature and reconstructing after annealing at 600°C. Germanium, being deposited from a molecular beam at room temperature on the Si(001) surface, forms a thin granular film composed of Ge particles with sizes of a few nanometers. A characteristic feature of these films is that they demonstrate signs of the 2 x 1 structure in their RHEED patterns. After short-term annealing at 600°C under the closed system conditions, the granular films reconstruct to heterostructures consisting of a Ge wetting layer and oval clusters of Ge. A mixed type c(4x2) + p(2x2) reconstruction typical to the low-temperature MBE (Tgr < 600°C) forms on the wetting layer. Long-term annealing of granular films at the same conditions results in formation of c(4x2)-reconstructed wetting layer typical to high-temperature MBE (Tgr < 600°C) and huge clusters of Ge. The other type of the studied nanostructures is based on Pt silicides. This class of materials is one of the friendliest to silicon technology. But as silicide film thickness reaches a few nanometers, low resistivity becomes of primary importance. Pt3Si has the lowest sheet resistance among the Pt silicides. However, the development of a process of thin Pt3Si films formation is a challenging task. This paper describes formation of a thin Pt3Si/Pt2Si structures at room temperature on poly-Si films. Special attention is paid upon formation of poly-Si and amorphous Si films on Si3N4 substrates at low temperatures.

Average irradiance and polarization properties of a radially or azimuthally polarized beam in a turbulent atmosphere.

PubMed

Cai, Yangjian; Lin, Qiang; Eyyuboğlu, Halil T; Baykal, Yahya

2008-05-26

Analytical formulas are derived for the average irradiance and the degree of polarization of a radially or azimuthally polarized doughnut beam (PDB) propagating in a turbulent atmosphere by adopting a beam coherence-polarization matrix. It is found that the radial or azimuthal polarization structure of a radially or azimuthally PDB will be destroyed (i.e., a radially or azimuthally PDB is depolarized and becomes a partially polarized beam) and the doughnut beam spot becomes a circularly Gaussian beam spot during propagation in a turbulent atmosphere. The propagation properties are closely related to the parameters of the beam and the structure constant of the atmospheric turbulence.

UQlust: combining profile hashing with linear-time ranking for efficient clustering and analysis of big macromolecular data.

PubMed

Adamczak, Rafal; Meller, Jarek

2016-12-28

Advances in computing have enabled current protein and RNA structure prediction and molecular simulation methods to dramatically increase their sampling of conformational spaces. The quickly growing number of experimentally resolved structures, and databases such as the Protein Data Bank, also implies large scale structural similarity analyses to retrieve and classify macromolecular data. Consequently, the computational cost of structure comparison and clustering for large sets of macromolecular structures has become a bottleneck that necessitates further algorithmic improvements and development of efficient software solutions. uQlust is a versatile and easy-to-use tool for ultrafast ranking and clustering of macromolecular structures. uQlust makes use of structural profiles of proteins and nucleic acids, while combining a linear-time algorithm for implicit comparison of all pairs of models with profile hashing to enable efficient clustering of large data sets with a low memory footprint. In addition to ranking and clustering of large sets of models of the same protein or RNA molecule, uQlust can also be used in conjunction with fragment-based profiles in order to cluster structures of arbitrary length. For example, hierarchical clustering of the entire PDB using profile hashing can be performed on a typical laptop, thus opening an avenue for structural explorations previously limited to dedicated resources. The uQlust package is freely available under the GNU General Public License at https://github.com/uQlust . uQlust represents a drastic reduction in the computational complexity and memory requirements with respect to existing clustering and model quality assessment methods for macromolecular structure analysis, while yielding results on par with traditional approaches for both proteins and RNAs.

Laser beam generating apparatus

DOEpatents

Warner, B.E.; Duncan, D.B.

1993-12-28

Laser beam generating apparatus including a septum segment disposed longitudinally within the tubular structure of the apparatus. The septum provides for radiatively dissipating heat buildup within the tubular structure and for generating relatively uniform laser beam pulses so as to minimize or eliminate radial pulse delays (the chevron effect). 11 figures.

Crustal velocity structure and earthquake processes of Garhwal-Kumaun Himalaya: Constraints from regional waveform inversion and array beam modeling

NASA Astrophysics Data System (ADS)

Negi, Sanjay S.; Paul, Ajay; Cesca, Simone; Kamal; Kriegerowski, Marius; Mahesh, P.; Gupta, Sandeep

2017-08-01

In order to understand present day earthquake kinematics at the Indian plate boundary, we analyse seismic broadband data recorded between 2007 and 2015 by the regional network in the Garhwal-Kumaun region, northwest Himalaya. We first estimate a local 1-D velocity model for the computation of reliable Green's functions, based on 2837 P-wave and 2680 S-wave arrivals from 251 well located earthquakes. The resulting 1-D crustal structure yields a 4-layer velocity model down to the depths of 20 km. A fifth homogeneous layer extends down to 46 km, constraining the Moho using travel-time distance curve method. We then employ a multistep moment tensor (MT) inversion algorithm to infer seismic moment tensors of 11 moderate earthquakes with Mw magnitude in the range 4.0-5.0. The method provides a fast MT inversion for future monitoring of local seismicity, since Green's functions database has been prepared. To further support the moment tensor solutions, we additionally model P phase beams at seismic arrays at teleseismic distances. The MT inversion result reveals the presence of dominant thrust fault kinematics persisting along the Himalayan belt. Shallow low and high angle thrust faulting is the dominating mechanism in the Garhwal-Kumaun Himalaya. The centroid depths for these moderate earthquakes are shallow between 1 and 12 km. The beam modeling result confirm hypocentral depth estimates between 1 and 7 km. The updated seismicity, constrained source mechanism and depth results indicate typical setting of duplexes above the mid crustal ramp where slip is confirmed along out-of-sequence thrusting. The involvement of Tons thrust sheet in out-of-sequence thrusting indicate Tons thrust to be the principal active thrust at shallow depth in the Himalayan region. Our results thus support the critical taper wedge theory, where we infer the microseismicity cluster as a result of intense activity within the Lesser Himalayan Duplex (LHD) system.

Photofragment slice imaging studies of pyrrole and the Xe…pyrrole cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubio-Lago, L.; Zaouris, D.; Sakellariou, Y.

The photolysis of pyrrole has been studied in a molecular beam at wavelengths 250 nm, 240 nm and 193.3 nm, using 2 different carrier gases, He and Xe. A broad bimodal distribution of H atom fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm, , sharp features have been observed in the fast part of the H-atom distribution. Under appropriate molecular beam conditions, these sharp features and the photolysis of pyrrole at both 240 and 250 nm disappear when using Xe as opposed to He as the carrier gas. We attribute this phenomenonmore » to cluster formation between Xe and pyrrole, and this assumption is supported by observation of resonance enhanced multiphoton ionization spectra for the (Xe…pyrrole) cluster followed by photofragmentation of the nascent cation cluster. Ab initio calculations are performed to support the experimental data. Part of this work is supported by the transfer of knowledge program SOUTHERN DYNAMICS MTKD-CT-2004-014306. The experimental work was performed at the Ultraviolet Laser Facility operating at IESL-FORTH and has been supported in part by the European Commission through the Research Infrastructures activity of FP6 (“Laserlab- Europe” RII3-CT-2003-506350). We also wish to thank the graduate program Applied Molecular Spectroscopy (EPEAEK). Part of this work was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, US Department of Energy with Battelle Memorial Institute, which operates the Pacific Northwest National Laboratory. Computer resources were provided by the Office of Science, US Department of Energy.« less

Monitoring of changes in cluster structures in water under AC magnetic field

NASA Astrophysics Data System (ADS)

Usanov, A. D.; Ulyanov, S. S.; Ilyukhina, N. S.; Usanov, D. A.

2016-01-01

A fundamental possibility of visualizing cluster structures formed in distilled water by an optical method based on the analysis of dynamic speckle structures is demonstrated. It is shown for the first time that, in contrast to the existing concepts, water clusters can be rather large (up to 200 -m in size), and their lifetime is several tens of seconds. These clusters are found to have an internal spatially inhomogeneous structure, constantly changing in time. The properties of magnetized and non-magnetized water are found to differ significantly. In particular, the number of clusters formed in magnetized water is several times larger than that formed in the same volume of non-magnetized water.

Determining the size dependence of structural properties of clusters

NASA Astrophysics Data System (ADS)

Dong, Yi; Springborg, Michael

2012-12-01

Problems related to the determination of the structure of the global total-energy minimum for clusters are discussed through three examples. For isolated gold clusters it is shown that low-symmetry structures result due to covalent bonding. Subsequently, SiNGeN and (HAlO)N clusters are treated for which the occurrence of so called homotops leads to additional computational complexity. For the former it is found that the structures are not directly related to those of the pure monatomic clusters, and for the latter the results are shown to be in agreement with available experimental information on nanostructured HAlO. In order to illustrate and analyze the results, various descriptors are introduced and applied.

Structures, stability and electronic properties of bimetallic Cun-1Sc and Cun-2Sc2 (n = 2-7) clusters

NASA Astrophysics Data System (ADS)

Li, Zhi; Zhao, Zhen; Zhou, Zhonghao; Wang, Qi

2018-02-01

To investigate the interface between the main phases of Cu-Sc alloys, the structures, stability and electronic properties of bimetallic Cun-1Sc and Cun-2Sc2 (n = 2-7) clusters are systematically calculated by the GGA-PW91 functional. The results reveal that the structures of Cun-1Sc and Cun-2Sc2 (n = 2-7) clusters inherited those of pure Cun (n = 2-7) clusters and they maintained higher symmetry. Cu5Sc cluster possesses more stable than its neighbors while Cu2Sc2 cluster is less stable than its neighbors by binding energy. Cu5Sc cluster possesses the highest kinetic stability of Cun-1Sc clusters and CuSc2, Cu3Sc2 and Cu5Sc2 clusters possess higher kinetic stability than their neighbors by HOMO-LUMO gap. NBO analysis reveals that Cu-Sc atoms have less pd orbital hybridization in the Sc doping Cun (n = 2-7) clusters.

Micro-heterogeneity versus clustering in binary mixtures of ethanol with water or alkanes.

PubMed

Požar, Martina; Lovrinčević, Bernarda; Zoranić, Larisa; Primorać, Tomislav; Sokolić, Franjo; Perera, Aurélien

2016-08-24

Ethanol is a hydrogen bonding liquid. When mixed in small concentrations with water or alkanes, it forms aggregate structures reminiscent of, respectively, the direct and inverse micellar aggregates found in emulsions, albeit at much smaller sizes. At higher concentrations, micro-heterogeneous mixing with segregated domains is found. We examine how different statistical methods, namely correlation function analysis, structure factor analysis and cluster distribution analysis, can describe efficiently these morphological changes in these mixtures. In particular, we explain how the neat alcohol pre-peak of the structure factor evolves into the domain pre-peak under mixing conditions, and how this evolution differs whether the co-solvent is water or alkane. This study clearly establishes the heuristic superiority of the correlation function/structure factor analysis to study the micro-heterogeneity, since cluster distribution analysis is insensitive to domain segregation. Correlation functions detect the domains, with a clear structure factor pre-peak signature, while the cluster techniques detect the cluster hierarchy within domains. The main conclusion is that, in micro-segregated mixtures, the domain structure is a more fundamental statistical entity than the underlying cluster structures. These findings could help better understand comparatively the radiation scattering experiments, which are sensitive to domains, versus the spectroscopy-NMR experiments, which are sensitive to clusters.

Vibration sensing method and apparatus

DOEpatents

Barna, B.A.

1989-04-25

A method and apparatus for nondestructive evaluation of a structure are disclosed. Resonant audio frequency vibrations are excited in the structure to be evaluated and the vibrations are measured and characterized to obtain information about the structure. The vibrations are measured and characterized by reflecting a laser beam from the vibrating structure and directing a substantial portion of the reflected beam back into the laser device used to produce the beam which device is capable of producing an electric signal containing information about the vibration. 4 figs.

Vibration sensing method and apparatus

DOEpatents

Barna, B.A.

1987-07-07

A method and apparatus for nondestructive evaluation of a structure is disclosed. Resonant audio frequency vibrations are excited in the structure to be evaluated and the vibrations are measured and characterized to obtain information about the structure. The vibrations are measured and characterized by reflecting a laser beam from the vibrating structure and directing a substantial portion of the reflected beam back into the laser device used to produce the beam which device is capable of producing an electric signal containing information about the vibration. 4 figs.

Vibration sensing method and apparatus

DOEpatents

Barna, Basil A.

1989-04-25

A method and apparatus for nondestructive evaluation of a structure is disclosed. Resonant audio frequency vibrations are excited in the structure to be evaluated and the vibrations are measured and characterized to obtain information about the structure. The vibrations are measured and characterized by reflecting a laser beam from the vibrating structure and directing a substantial portion of the reflected beam back into the laser device used to produce the beam which device is capable of producing an electric signal containing information about the vibration.

From the Superatom Model to a Diverse Array of Super-Elements: A Systematic Study of Dopant Influence on the Electronic Structure of Thiolate-Protected Gold Clusters.

PubMed

Schacht, Julia; Gaston, Nicola

2016-10-18

The electronic properties of doped thiolate-protected gold clusters are often referred to as tunable, but their study to date, conducted at different levels of theory, does not allow a systematic evaluation of this claim. Here, using density functional theory, the applicability of the superatomic model to these clusters is critically evaluated, and related to the degree of structural distortion and electronic inhomogeneity in the differently doped clusters, with dopant atoms Pd, Pt, Cu, and Ag. The effect of electron number is systematically evaluated by varying the charge on the overall cluster, and the nominal number of delocalized electrons, employed in the superatomic model, is compared to the numbers obtained from Bader analysis of individual atomic charges. We find that the superatomic model is highly applicable to all of these clusters, and is able to predict and explain the changing electronic structure as a function of charge. However, significant perturbations of the model arise due to doping, due to distortions of the core structure of the Au 13 [RS(AuSR) 2 ] 6 - cluster. In addition, analysis of the electronic structure indicates that the superatomic character is distributed further across the ligand shell in the case of the doped clusters, which may have implications for the self-assembly of these clusters into materials. The prediction of appropriate clusters for such superatomic solids relies critically on such quantitative analysis of the tunability of the electronic structure. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Further Development of Ko Displacement Theory for Deformed Shape Predictions of Nonuniform Aerospace Structures

NASA Technical Reports Server (NTRS)

Ko, William L.; Fleischer, Van Tran

2009-01-01

The Ko displacement theory previously formulated for deformed shape predictions of nonuniform beam structures is further developed mathematically. The further-developed displacement equations are expressed explicitly in terms of geometrical parameters of the beam and bending strains at equally spaced strain-sensing stations along the multiplexed fiber-optic sensor line installed on the bottom surface of the beam. The bending strain data can then be input into the displacement equations for calculations of local slopes, deflections, and cross-sectional twist angles for generating the overall deformed shapes of the nonuniform beam. The further-developed displacement theory can also be applied to the deformed shape predictions of nonuniform two-point supported beams, nonuniform panels, nonuniform aircraft wings and fuselages, and so forth. The high degree of accuracy of the further-developed displacement theory for nonuniform beams is validated by finite-element analysis of various nonuniform beam structures. Such structures include tapered tubular beams, depth-tapered unswept and swept wing boxes, width-tapered wing boxes, and double-tapered wing boxes, all under combined bending and torsional loads. The Ko displacement theory, combined with the fiber-optic strain-sensing system, provide a powerful tool for in-flight deformed shape monitoring of unmanned aerospace vehicles by ground-based pilots to maintain safe flights.

Structures of 38-atom gold-platinum nanoalloy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ong, Yee Pin; Yoon, Tiem Leong; Lim, Thong Leng

2015-04-24

Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, Au{sub n}Pt{sub 38−n} (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atomsmore » are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature.« less

Cluster synchronization induced by one-node clusters in networks with asymmetric negative couplings

NASA Astrophysics Data System (ADS)

Zhang, Jianbao; Ma, Zhongjun; Zhang, Gang

2013-12-01

This paper deals with the problem of cluster synchronization in networks with asymmetric negative couplings. By decomposing the coupling matrix into three matrices, and employing Lyapunov function method, sufficient conditions are derived for cluster synchronization. The conditions show that the couplings of multi-node clusters from one-node clusters have beneficial effects on cluster synchronization. Based on the effects of the one-node clusters, an effective and universal control scheme is put forward for the first time. The obtained results may help us better understand the relation between cluster synchronization and cluster structures of the networks. The validity of the control scheme is confirmed through two numerical simulations, in a network with no cluster structure and in a scale-free network.

The X-ray structure of a galaxy cluster at z = 0.54 - Implications for cluster evolution and cosmology

NASA Technical Reports Server (NTRS)

White, S. D. M.; Silk, J.; Henry, J. P.

1981-01-01

High-resolution X-ray observations of the rich cluster 0016+16 at a redshift of 0.541 are presented. The emitting gas in this cluster is hot and extremely luminous, and its structure resembles that seen in the brightest nearby cluster sources. In most of its properties, 0016+16 resembles a richer version of the Coma cluster, and it offers little support to the hypothesis that clusters at z greater than 0.5 differ fundamentally from nearer objects.

The high-field magnet endstation for X-ray magnetic dichroism experiments at ESRF soft X-ray beamline ID32.

PubMed

Kummer, K; Fondacaro, A; Jimenez, E; Velez-Fort, E; Amorese, A; Aspbury, M; Yakhou-Harris, F; van der Linden, P; Brookes, N B

2016-03-01

A new high-field magnet endstation for X-ray magnetic dichroism experiments has been installed and commissioned at the ESRF soft X-ray beamline ID32. The magnet consists of two split-pairs of superconducting coils which can generate up to 9 T along the beam and up to 4 T orthogonal to the beam. It is connected to a cluster of ultra-high-vacuum chambers that offer a comprehensive set of surface preparation and characterization techniques. The endstation and the beam properties have been designed to provide optimum experimental conditions for X-ray magnetic linear and circular dichroism experiments in the soft X-ray range between 400 and 1600 eV photon energy. User operation started in November 2014.

Analysis of TOF-SIMS spectra from fullerene compounds

NASA Astrophysics Data System (ADS)

Kato, N.; Yamashita, Y.; Iida, S.; Sanada, N.; Kudo, M.

2008-12-01

We analyzed TOF-SIMS spectra obtained from three different size of fullerenes (C 60, C 70 and C 84) by using Ga +, Au + and Au 3+ primary ion beams and investigated the fragmentation patterns, the enhancement of secondary ion yields and the restraint of fragmentation by using cluster primary ion beams compared with monoatomic primary ion beams. In the TOS-SIMS spectra from C 70 and C 84, it was found that a fragment ion, identified as C 60+ ( m/ z = 720), showed a relatively high intensity compared with that of other fragment ions related to C 2 depletion. It was also found that the Au 3+ bombardment caused intensity enhancement of intact molecules (C 60+, C 70+ and C 84+) and restrained the fragmentation due to C 2 depletion.

Using a plenoptic sensor to reconstruct vortex phase structures.

PubMed

Wu, Chensheng; Ko, Jonathan; Davis, Christopher C

2016-07-15

A branch point problem and its solution commonly involve recognizing and reconstructing a vortex phase structure around a singular point. In laser beam propagation through random media, the destructive phase contributions from various parts of a vortex phase structure will cause a dark area in the center of the beam's intensity profile. This null of intensity can, in turn, prevent the vortex phase structure from being recognized. In this Letter, we show how to use a plenoptic sensor to transform the light field of a vortex beam so that a simple and direct reconstruction algorithm can be applied to reveal the vortex phase structure. As a result, we show that the plenoptic sensor is effective in detecting branch points and can be used to reconstruct phase distortion in a beam in a wide sense.

Lowest-energy structures and electronic properties of Na-Si binary clusters from ab initio global search.

PubMed

Sai, Linwei; Tang, Lingli; Zhao, Jijun; Wang, Jun; Kumar, Vijay

2011-11-14

The ground state structures of neutral and anionic clusters of Na(n)Si(m) (1 ≤ n ≤ 3, 1 ≤ m ≤ 11) have been determined using genetic algorithm incorporated in first principles total energy code. The size dependence of the structural and electronic properties is discussed in detail. It is found that the lowest-energy structures of Na(n)Si(m) clusters resemble those of the pure Si clusters. Interestingly, Na atoms in neutral Na(n)Si(m) clusters are usually well separated by the Si(m) skeleton, whereas Na atoms can form Na-Na bonds in some anionic clusters. The ionization potentials, adiabatic electron affinities, and photoelectron spectra are also calculated and the results compare well with the experimental data. © 2011 American Institute of Physics

Ab initio structures and polarizabilities of sodium clusters

NASA Astrophysics Data System (ADS)

Kronik, Leeor; Vasiliev, Igor; Jain, Manish; Chelikowsky, James R.

2001-09-01

We present quantitative ab initio calculations for Na cluster structures and polarizabilities, for all cluster sizes up to 20 atoms. Our calculations are performed by combining an ab initio core-corrected pseudopotential and a gradient-corrected density functional within a real space approach. We find the cluster bonding to be very floppy and catalog a host of low-energy quasi-degenerate isomers for all second-decade clusters. The existence of these isomers results in a band of polarizability values for each cluster size even at zero temperature. This eliminates any finer structure in the polarizability curve. We further show that the experimental polarizability values are consistently underestimated by calculations at zero temperature. By computing the effects of structure expansion and distortion due to a finite temperature we arrive at a quantitative agreement between theory and experiment.

Influence of syllable structure on L2 auditory word learning.

PubMed

Hamada, Megumi; Goya, Hideki

2015-04-01

This study investigated the role of syllable structure in L2 auditory word learning. Based on research on cross-linguistic variation of speech perception and lexical memory, it was hypothesized that Japanese L1 learners of English would learn English words with an open-syllable structure without consonant clusters better than words with a closed-syllable structure and consonant clusters. Two groups of college students (Japanese group, N = 22; and native speakers of English, N = 21) learned paired English pseudowords and pictures. The pseudoword types differed in terms of the syllable structure and consonant clusters (congruent vs. incongruent) and the position of consonant clusters (coda vs. onset). Recall accuracy was higher for the pseudowords in the congruent type and the pseudowords with the coda-consonant clusters. The syllable structure effect was obtained from both participant groups, disconfirming the hypothesized cross-linguistic influence on L2 auditory word learning.

Thermal stability of Pt nanoclusters interacting to carbon sublattice

NASA Astrophysics Data System (ADS)

Baidyshev, V. S.; Gafner, Yu. Ya.; Gafner, S. L.; Redel, L. V.

2017-12-01

The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of "free" Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter D ≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.

Laser beam generating apparatus

DOEpatents

Warner, B.E.; Duncan, D.B.

1994-02-15

Laser beam generating apparatus including a septum segment disposed longitudinally within the tubular structure of the apparatus is described. The septum provides for radiatively dissipating heat buildup within the tubular structure and for generating relatively uniform laser beam pulses so as to minimize or eliminate radial pulse delays (the chevron effect). 7 figures.

Development of Mid-infrared GeSn Light Emitting Diodes on a Silicon Substrate

DTIC Science & Technology

2015-04-22

Materials, Heterostrucuture Semiconductor, Light Emitting Devices, Molecular Beam Epitaxy 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT...LED) structure. Optimization of traditional and hetero- P-i-N structures designed and grown on Ge-buffer Si (001) wafers using molecular beam epitaxy ...designed structures were grown on Ge-buffer Si (001) wafers using molecular beam epitaxy (MBE) with the low-temperature growth technique. (The Ge-buffer

Proton beam writing of long, arbitrary structures for micro/nano photonics and fluidics applications

NASA Astrophysics Data System (ADS)

Udalagama, Chammika; Teo, E. J.; Chan, S. F.; Kumar, V. S.; Bettiol, A. A.; Watt, F.

2011-10-01

The last decade has seen proton beam writing maturing into a versatile lithographic technique able to produce sub-100 nm, high aspect ratio structures with smooth side walls. However, many applications in the fields of photonics and fluidics require the fabrication of structures with high spatial resolution that extends over several centimetres. This cannot be achieved by purely magnetic or electrostatic beam scanning due to the large off-axis beam aberrations in high demagnification systems. As a result, this has limited us to producing long straight structures using a combination of beam and stage scanning. In this work we have: (1) developed an algorithm to include any arbitrary pattern into the writing process by using a more versatile combination of beam and stage scanning while (2) incorporating the use of the ubiquitous AutoCAD DXF (drawing exchange format) into the design process. We demonstrate the capability of this approach in fabricating structures such as Y-splitters, Mach-Zehnder modulators and microfluidic channels that are over several centimetres in length, in polymer. We also present optimisation of such parameters as scanning speed and scanning loops to improve on the surface roughness of the structures. This work opens up new possibilities of using CAD software in PBW for microphotonics and fluidics device fabrication.

In Situ formation of microstructures near live cells using spatially structured near-infrared laser microbeam

NASA Astrophysics Data System (ADS)

Ingle, Ninad; Gu, Ling; Mohanty, Samarendra K.

2011-03-01

Here, we report in situ formation of microstructures from the regular constituents of culture media near live cells using spatially-structured near infrared (NIR) laser beam. Irradiation with the continuous wave (cw) NIR laser microbeam for few seconds onto the regular cell culture media containing fetal bovine serum resulted in accumulation of dense material inside the media as evidenced by phase contrast microscopy. The time to form the phase dense material was found to depend on the laser beam power. Switching off the laser beam led to diffusion of phase dark material. However, the proteins could be stitched together by use of carbon nanoparticles and continuous wave (cw) Ti: Sapphire laser beam. Further, by use of spatially-structured beam profiles different structures near live cells could be formed. The microfabricated structure could be held by the Gravito-optical trap and repositioned by movement of the sample stage. Orientation of these microstructures was achieved by rotating the elliptical laser beam profile. Thus, multiple microstructures were formed and organized near live cells. This method would enable study of response of cells/axons to the immediate physical hindrance provided by such structure formation and also eliminate the biocompatibility requirement posed on artificial microstructure materials.

Effect of ion beam irradiation on the structure of ZnO films deposited by a dc arc plasmatron.

PubMed

Penkov, Oleksiy V; Lee, Heon-Ju; Plaksin, Vadim Yu; Ko, Min Gook; Joa, Sang Beom; Yim, Chan Joo

2008-02-01

The deposition of polycrystalline ZnO film on a cold substrate was performed by using a plasmatron in rough vacuum condition. Low energy oxygen ion beam generated by a cold cathode ion source was introduced during the deposition process. The change of film property on the ion beam energy was checked. It is shown that irradiation by 200 eV ions improves crystalline structure of the film. Increasing of ion beam energy up to 400 eV leads to the degradation of a crystalline structure and decreases the deposition rate.

Structures of Aln (n= 27, 28, 29, and 30) clusters with double-tetrahedron structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, W.; Lu, W. C.; Sun, J.

2008-01-31

Global search for lowest-energy structures of neutral aluminum clusters Al{sub n} (n = 27, 28, 29 and 30) was performed using a genetic algorithm (GA) coupled with a tight-binding (TB) method. Structural candidates obtained from our GA search were further optimized with first-principles calculations. It is found that the medium-sized aluminum clusters Al{sub 27} to Al{sub 30} favor double-tetrahedron structures.