scholarly journals A Method of Determining Channeling Parameters in Backscattering Geometry

2019 ◽  
Vol 7 ◽  
pp. 122
Author(s):  
M. Kokkoris ◽  
S. Kossionides ◽  
T. Paradellis ◽  
Ch. Zarkadas ◽  
E. N. Gazis ◽  
...  
Keyword(s):  
Energy Loss ◽  
Resonance Phenomenon ◽  
Experimental Setup ◽  
Nuclear Resonance ◽  
Monte Carlo Calculations ◽  
The Past ◽  
Transmission Geometry ◽  
Good Agreement

The energy loss of channeled protons in silicon has been measured in the past in the transmission geometry and was found to be approximately half of the normal loss, thus confirming the equipartition rule. Other measurements however, concerning different crystals (e.g. Ge), deviated from this theory. In the backscattering geometry, the most successful corresponding attempts combined RBS with the nuclear resonance phenomenon. Nevertheless, they involved ether considerable additions to the standard goniometer setup commonly used, or tedious Monte-Carlo calculations, thus limiting their applicability. ïïi the present work, a method for the determination of the energy loss and dechanneling probabilities of axially channeled protons in silicon [100], in the energy range Ep = 1.7-2.6 MeV, is presented. It is carried out in situ, using the same experimental setup and beam properties (size, divergence) with the ones present in the actual analysis of a sample. The results obtained are in good agreement with already existing values in literature.

scholarly journals Structure Determination of Microtubules and Pili: Past, Present, and Future Directions

2022 ◽  
Vol 8 ◽  
Author(s):  
James A. Garnett ◽  
Joseph Atherton
Keyword(s):  
Ex Vivo ◽  
Structural Heterogeneity ◽  
Resonance Spectroscopy ◽  
Future Directions ◽  
Computational Approaches ◽  
The Past ◽  
Major Shift ◽  
Technical Innovations

Historically proteins that form highly polymeric and filamentous assemblies have been notoriously difficult to study using high resolution structural techniques. This has been due to several factors that include structural heterogeneity, their large molecular mass, and available yields. However, over the past decade we are now seeing a major shift towards atomic resolution insight and the study of more complex heterogenous samples and in situ/ex vivo examination of multi-subunit complexes. Although supported by developments in solid state nuclear magnetic resonance spectroscopy (ssNMR) and computational approaches, this has primarily been due to advances in cryogenic electron microscopy (cryo-EM). The study of eukaryotic microtubules and bacterial pili are good examples, and in this review, we will give an overview of the technical innovations that have enabled this transition and highlight the advancements that have been made for these two systems. Looking to the future we will also describe systems that remain difficult to study and where further technical breakthroughs are required.

In situobservation of morphological changes of γ′ precipitates in a pre-deformed single-crystal Ni-base superalloy

2011 ◽  
Vol 44 (5) ◽  
pp. 935-944 ◽  
Author(s):  
Pavel Strunz ◽  
Gerhard Schumacher ◽  
Hellmuth Klingelhöffer ◽  
Albrecht Wiedenmann ◽  
Jan Šaroun ◽  
...  
Keyword(s):  
External Load ◽  
Morphological Changes ◽  
The Past ◽  
Subsequent Heating ◽  
Detailed Evaluation ◽  
The Matrix ◽  
Base Superalloy

Exposure of a superalloy to an external load results in anisotropic coarsening of the γ′ precipitates, so-called rafting. It was reported in the past that γ′ rafting can also occur as a result of purely thermal treatment, without the simultaneous presence of an external load, if the specimen has been pre-deformed at relatively low temperature. The evolution of γ′ morphology in pre-deformed specimens of SCA425 Ni-base superalloy was examined in the present study. Unlike in the previous experiments, the compressive stress was used for pre-straining.In situsmall-angle neutron scattering (SANS) was employed, which enabled the determination of the morphology directly at high temperature. Both for strong and for weak pre-straining, rounding of the originally cuboidal precipitates towards an ellipsoidal shape on heating was observed. Weak pre-straining (0.1, 0.5%) does not cause rafting on subsequent heating. On the other hand, the detailed evaluation of SANS data provides some indication of rafting during the subsequent heating after severe compressive pre-straining (2%). The experiment indicates the role of dislocation rearrangement at the matrix/precipitate interface during pre-straining.

A Six-Degree-of-Freedom Test System for the Study of Joint Mechanics and Ligament Forces

1995 ◽  
Vol 117 (4) ◽  
pp. 383-389 ◽  
Author(s):  
J. M. Hollis
Keyword(s):  
Degrees Of Freedom ◽  
Test System ◽  
Testing System ◽  
Joint Mechanics ◽  
Six Degrees Of Freedom ◽  
Position Feedback ◽  
Six Degree Of Freedom ◽  
Good Agreement

A joint testing system was designed to transmit a specified motion or force to a joint in all six degrees of freedom (d.o.f.) using a spatial linkage system for position feedback. The precise reproducibility of position provided by this method of position feedback allows determination of in situ ligament forces for external joint loadings. Load on the structure of interest is calculated from six d.o.f. load cell output after the loaded position is reproduced with all other structures removed. In a test of this system, measured loads showed good agreement with applied loads.

Determination of the Roughness of CVD Surfaces by Laser Scattering

1991 ◽  
Vol 250 ◽  
Author(s):  
Max Klein ◽  
Bernard Gallois
Keyword(s):  
Scattered Light ◽  
Spatial Arrangement ◽  
Ex Situ ◽  
Root Mean Square Roughness ◽  
Statistical Parameters ◽  
Laser Scattering ◽  
Light Spectra ◽  
Good Agreement

AbstractA laser scattering apparatus was developed for the determination of surface roughness and other surface statistical parameters of chemically vapor-deposited coatings. Visual examination of HeNe laser scattering patterns reflected from polished sapphire and CVD titanium nitride surfaces showed a sensitivity to roughness differences of tens of nanometers. The scattering apparatus was integrated with a cold-wall CVD reactor. The root mean square roughness of silicon carbide deposits on silicon in the early stages of growth was determined from the intensity of the specularly reflected beam. Changes in roughness and the spatial arrangement of depositing crystallites were monitored in situ by angular resolution of the scattered light spectra. Both ex situ and in situ results were in good agreement with profilometric examinations of the rough surfaces.

In Situ Synchrotron Measurements of Oxide Growth Strains

2005 ◽  
Vol 490-491 ◽  
pp. 287-293 ◽  
Author(s):  
Jonathan Almer ◽  
Geoffrey A. Swift ◽  
John A. Nychka ◽  
Ersan Üstündag ◽  
David R. Clarke
Keyword(s):  
Strain Relaxation ◽  
Relaxation Mechanism ◽  
High Energy ◽  
Oxide Growth ◽  
X Rays ◽  
Pure Alumina ◽  
Transmission Geometry ◽  
Residual Strains

Synchrotron x-rays are used for in situ determination of oxide strain, during oxide formation on a Kanthal A1 FeCrAlZr substrate at 1160°C. The measurements rely on use of high-energy (~80keV) x-rays and transmission geometry, and the methodology of the strain measurements is presented. Oxide growth strains at elevated temperature, relative to pure alumina, were seen to be small, while temperature excursions induced significant strains. Furthermore, significant strain relaxation was observed during isothermal holds, suggesting oxide creep as a major relaxation mechanism. Upon cooling to room temperature, significant residual strains developed, with a corresponding in-plane residual stress of -3.7 GPa.

scholarly journals Measurements of Energy Loss of Charded Particles Travelling in Crystalline Materials along the Channeling Directon

2021 ◽  
Vol 12 ◽  
pp. 82
Author(s):  
M. Kokkoris ◽  
R. Vlastou ◽  
C. T. Papadopoulos ◽  
X. Aslanoglou ◽  
S. Kossionides ◽  
...  
Keyword(s):  
Energy Loss ◽  
Computer Simulations ◽  
Charged Particles ◽  
Crystalline Material ◽  
Nuclear Resonance ◽  
Exponential Rate ◽  
Crystalline Materials ◽  
Resonance Reactions ◽  
Light Charged Particles ◽  
Good Agreement

A method for determining the energy loss and mean dechanneling distance of light charged particles traveling along a low index axis of a crystal in the backscattering geometry, is presented. The method is based on nuclear resonance reactions which act as a marker for the range in the backscattering spectra. Computer simulations based on the assumption of an exponential rate of dechanneling of the incoming particles in the crystalline material, are in good agreement with measured spectra. The results of applying this method to protons and alphas in crystals of Si, SiO2, SiC and MgO are discussed and possible improvements are indicated.

scholarly journals Determination of effective atomic numbers and electron densities from mass attenuation coefficients for some selected complexes containing lanthanides

2017 ◽  
Vol 95 (10) ◽  
pp. 1005-1011 ◽  
Author(s):  
Ferdi Akman ◽  
Mustafa Recep Kaçal ◽  
Feride Akman ◽  
Mustafa Serkan Soylu
Keyword(s):  
Chemical Parameters ◽  
Electron Densities ◽  
Attenuation Coefficients ◽  
Transmission Geometry ◽  
Mass Attenuation Coefficients ◽  
Effective Atomic Numbers ◽  
Theoretical Results ◽  
Good Agreement ◽  
Mass Attenuation

The effective atomic numbers and electron densities for the pure elemental forms of gadolinium (Gd), dysprosium (Dy), erbium (Er), and ytterbium (Yb), and some of their selected complexes, were obtained from the measured total mass attenuation coefficients at 13.92, 17.75, 20.78, 26.34, and 59.54 keV photon energies using a high-resolution Si(Li) detector by adopting transmission geometry. The measured results were compared with two different theoretical results. Within experimental deviations, our data are in good agreement with the theoretical values. The obtained parameters were also interpreted with some selected chemical parameters.

Time-of-flight neutron transmission diffraction

2001 ◽  
Vol 34 (3) ◽  
pp. 289-297 ◽  
Author(s):  
J. R. Santisteban ◽  
L. Edwards ◽  
A. Steuwer ◽  
P. J. Withers
Keyword(s):  
Time Of Flight ◽  
Neutron Transmission ◽  
Lattice Strains ◽  
Nickel Powders ◽  
Transmission Geometry ◽  
Spallation Source ◽  
The Uk ◽  
Pulsed Neutron

The positions of Bragg edges in neutron transmission experiments can be defined with high accuracy using the time-of-flight (TOF) technique on pulsed neutron sources. A new dedicated transmission instrument has been developed at ISIS, the UK spallation source, which provides a precision of Δd/d≃ 10−5in the determination of interplanar distances. This is achieved by fitting a theoretical three-parameter expression to the normalized Bragg edges appearing in the TOF transmission spectra. The technique is demonstrated by experiments performed on iron, niobium and nickel powders. The applicability of using the instrument for the determination of lattice strains in materials has been investigated using a simplein situloading experiment. Details of the calibration process are presented and the dependence of the resolution and the experimental times required by the transmission geometry on the instrumental variables are studied. Finally, the requirements for a Rietveld-type refinement of transmission data and the advantages and limitations over traditional neutron diffraction peak analysis are discussed.

Monte-Carlo-Rechnungen und Messungen zur Vielfachstreuung von schweren Ionen in dünnen Folien / Monte Carlo Calculations and Measurements Concerning the Multiple Scattering of Heavy Ions in Thin Films

1976 ◽  
Vol 31 (8) ◽  
pp. 949-955 ◽  
Author(s):  
J. Zienert ◽  
K. Güttner ◽  
G. Münzenberg
Keyword(s):  
Thin Films ◽  
Monte Carlo ◽  
Monte Carlo Method ◽  
Energy Loss ◽  
Heavy Ions ◽  
Energy Distributions ◽  
Monte Carlo Calculations ◽  
Screening Parameter ◽  
Screened Coulomb Potential ◽  
Good Agreement

Abstract The behaviour of energetic heavy ions in thin films is simulated by means of a Monte Carlo method taking especially into account the energy loss of the scattered particles. Based on a variably matched screened Coulomb potential the calculations yield the angular and energy distributions of the transmitted ions. The results show a good agreement with the theory of Meyer. Furthermore for keV He ions scattering distributions have been measured in C, Al and Ag, which agree fairly well with the computations, if a suitable fit of the screening parameter is used in the Monte Carlo simulations.

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