Time-of-flight neutron transmission of mosaic crystals

2005 ◽  
Vol 38 (6) ◽  
pp. 934-944 ◽  
Author(s):  
Javier R. Santisteban
Keyword(s):  
Crystal Orientation ◽  
Average Rate ◽  
Time Of Flight ◽  
Incident Beam ◽  
Linear Increase ◽  
Reflection Index ◽  
Neutron Transmission ◽  
Mosaic Crystals ◽  
Definition Of

The energy-dispersive neutron transmission of mosaic crystals presents a series of dips in intensity as a result of reflection in the crystal planes. The positions of these dips can be exploited for the definition of the crystal orientation with a resolution of 1 min of arc. The widths of these dips depend on crystal orientation, on the reflection index, on the mosaicity, and on the incident-beam divergence. The capability of the technique to define the orientation and mosaicity of a Cu crystal has been assessed through time-of-flight experiments. A Cu monochromator has been plastically deformed by uniaxial tensionin situ, and the evolution of crystal orientation and mosaicity was tracked using the technique. Several crystal reflections at different locations of the sample were simultaneously studied during the experiment. A linear increase of mosaicity on deformation at an average rate of ∼5 min per percentage of shear strain was observed. The reorientation of the crystal as a result of the applied load showed variations across the specimen.

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.

In situdetermination of stresses from time-of-flight neutron transmission spectra

2003 ◽  
Vol 36 (5) ◽  
pp. 1159-1168 ◽  
Author(s):  
Axel Steuwer ◽  
Javier Roberto Santisteban ◽  
Philip J. Withers ◽  
Lyndon Edwards ◽  
Mike E. Fitzpatrick
Keyword(s):  
Elastic Anisotropy ◽  
Time Of Flight ◽  
Lattice Parameter ◽  
Polycrystalline Materials ◽  
Uniaxial Tensile ◽  
Transmission Spectra ◽  
X Ray Diffraction ◽  
Neutron Transmission ◽  
Pulsed Neutron

The pulsed neutron transmission diffraction technique exploits the sharp steps in intensity (Bragg edges) appearing in the transmitted spectra of thermal neutrons through polycrystalline materials. In this paper the positions of these edges acquired by the time-of-flight (TOF) technique are used to measure accurately the interplanar lattice distances to a resolution of Δd/d≃ 10−4of specimens subjected toin situuniaxial tensile loading. The sensitivity of the method is assessed for elastically isotropic (b.c.c. ferritic) and anisotropic (f.c.c. austenitic) polycrystalline specimens of negligible and moderately textured steels. For the more anisotropic austenitic steel, the elastic anisotropy is studied with regard to a Pawley refinement, and compared with previous results from conventional neutron diffraction experiments on the same material. It is shown that the method can be used to determine anisotropic strains, diffraction elastic constants, the residual and applied stress state as well as the unstrained lattice parameter by recording transmission spectra at different specimen inclinations, by complete analogy with the sin2ψ technique frequently used in X-ray diffraction. The technique is shown to deliver reliable measures of strain even in the case of moderate texture and elastic anisotropy.

Optics-Free Visualization of Proteins in Single Cells by Time of Flight-Secondary Ion Mass Spectrometry Coupled with Genetically Encoded Chemical Tags

2020 ◽  
Author(s):  
Feifei Jia ◽  
Jie Wang ◽  
Yanyan Zhang ◽  
Qun Luo ◽  
Luyu Qi ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Single Cells ◽  
Time Of Flight ◽  
E Coli ◽  
Tof Sims ◽  
Ion Mass Spectrometry ◽  
Chemical Tags ◽  
Secondary Ion

<p></p><p><i>In situ</i> visualization of proteins of interest at single cell level is attractive in cell biology, molecular biology and biomedicine, which usually involves photon, electron or X-ray based imaging methods. Herein, we report an optics-free strategy that images a specific protein in single cells by time of flight-secondary ion mass spectrometry (ToF-SIMS) following genetic incorporation of fluorine-containing unnatural amino acids as a chemical tag into the protein via genetic code expansion technique. The method was developed and validated by imaging GFP in E. coli and human HeLa cancer cells, and then utilized to visualize the distribution of chemotaxis protein CheA in E. coli cells and the interaction between high mobility group box 1 protein and cisplatin damaged DNA in HeLa cells. The present work highlights the power of ToF-SIMS imaging combined with genetically encoded chemical tags for <i>in situ </i>visualization of proteins of interest as well as the interactions between proteins and drugs or drug damaged DNA in single cells.</p><p></p>

scholarly journals Identification of effective spreaders in contact networks using dynamical influence

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Ruaridh A. Clark ◽  
Malcolm Macdonald
Keyword(s):  
Disease Transmission ◽  
Average Rate ◽  
Laplacian Matrix ◽  
Disease Spread ◽  
Eigenvector Centrality ◽  
Contact Networks ◽  
Human Contact ◽  
Spread Dynamics ◽  
Definition Of ◽  
High Degree

AbstractContact networks provide insights on disease spread due to the duration of close proximity interactions. For systems governed by consensus dynamics, network structure is key to optimising the spread of information. For disease spread over contact networks, the structure would be expected to be similarly influential. However, metrics that are essentially agnostic to the network’s structure, such as weighted degree (strength) centrality and its variants, perform near-optimally in selecting effective spreaders. These degree-based metrics outperform eigenvector centrality, despite disease spread over a network being a random walk process. This paper improves eigenvector-based spreader selection by introducing the non-linear relationship between contact time and the probability of disease transmission into the assessment of network dynamics. This approximation of disease spread dynamics is achieved by altering the Laplacian matrix, which in turn highlights why nodes with a high degree are such influential disease spreaders. From this approach, a trichotomy emerges on the definition of an effective spreader where, for susceptible-infected simulations, eigenvector-based selections can either optimise the initial rate of infection, the average rate of infection, or produce the fastest time to full infection of the network. Simulated and real-world human contact networks are examined, with insights also drawn on the effective adaptation of ant colony contact networks to reduce pathogen spread and protect the queen ant.

scholarly journals Experimental Evaluation of Shear Behavior of Stone Masonry Wall

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2313
Author(s):  
Maria Luisa Beconcini ◽  
Pietro Croce ◽  
Paolo Formichi ◽  
Filippo Landi ◽  
Benedetta Puccini
Keyword(s):  
Shear Behavior ◽  
Stone Masonry ◽  
Masonry Walls ◽  
Mechanical Parameters ◽  
In Situ Tests ◽  
Capacity Curves ◽  
Historical Structures ◽  
Definition Of

The evaluation of the shear behavior of masonry walls is a first fundamental step for the assessment of existing masonry structures in seismic zones. However, due to the complexity of modelling experimental behavior and the wide variety of masonry types characterizing historical structures, the definition of masonry’s mechanical behavior is still a critical issue. Since the possibility to perform in situ tests is very limited and often conflicting with the needs of preservation, the characterization of shear masonry behavior is generally based on reference values of mechanical properties provided in modern structural codes for recurrent masonry categories. In the paper, a combined test procedure for the experimental characterization of masonry mechanical parameters and the assessment of the shear behavior of masonry walls is presented together with the experimental results obtained on three stone masonry walls. The procedure consists of a combination of three different in situ tests to be performed on the investigated wall. First, a single flat jack test is executed to derive the normal compressive stress acting on the wall. Then a double flat jack test is carried out to estimate the elastic modulus. Finally, the proposed shear test is performed to derive the capacity curve and to estimate the shear modulus and the shear strength. The first results obtained in the experimental campaign carried out by the authors confirm the capability of the proposed methodology to assess the masonry mechanical parameters, reducing the uncertainty affecting the definition of capacity curves of walls and consequently the evaluation of seismic vulnerability of the investigated buildings.

In Situ Preparation and Mechanical Properties of (ZrB2+ZrC)/Zr3[Al(Si)]4C6 Composites

2014 ◽  
Vol 602-603 ◽  
pp. 438-442
Author(s):  
Lei Yu ◽  
Jian Yang ◽  
Tai Qiu
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Bending Strength ◽  
Coefficient Of Thermal Expansion ◽  
Raw Materials ◽  
Linear Increase ◽  
Fine Grain ◽  
Fine Grain Strengthening ◽  
Uniform Microstructure

Fully dense (ZrB2+ZrC)/Zr3[Al (Si)]4C6 composites with ZrB2 content varying from 0 to 15 vol.% and fixed ZrC content of 10 vol.% were successfully prepared by in situ hot-pressing in Ar atmosphere using ZrH2, Al, Si, C and B4C as raw materials. With the increase of ZrB2 content, both the bending strength and fracture toughness of the composites increase and then decrease. The synergistic action of ZrB2 and ZrC as reinforcements shows significant strengthening and toughing effect to the Zr3[Al (Si)]4C6 matrix. The composite with 10 vol.% ZrB2 shows the optimal mechanical properties: 516 MPa for bending strength and 6.52 MPa·m1/2 for fracture toughness. With the increase of ZrB2 content, the Vickers hardness of the composites shows a near-linear increase from 15.3 GPa to 16.7 GPa. The strengthening and toughening effect can be ascribed to the unique mechanical properties of ZrB2 and ZrC reinforcements, the differences in coefficient of thermal expansion and modulus between them and Zr3[Al (Si)]4C6 matrix, fine grain strengthening and uniform microstructure derived by the in situ synthesis reaction.

Influence of length and sensor positioning on acoustic time-of-flight (ToF) measurement in structural timber

Holzforschung ◽  
2017 ◽  
Vol 71 (9) ◽  
pp. 713-723 ◽  
Author(s):  
Francisco Arriaga ◽  
Daniel F. Llana ◽  
Miguel Esteban ◽  
Guillermo Íñiguez-González
Keyword(s):  
Time Lag ◽  
Time Of Flight ◽  
Radiata Pine ◽  
Apparent Velocity ◽  
Longitudinal Measurements ◽  
Dependent Property ◽  
Length Determination ◽  
End To End ◽  
Sensor Positioning

Abstract The mechanical properties of timber can be estimated from wave propagation velocity by measuring wave time-of-flight (ToF). However, a time-lag complicates the measurements, which produces an apparent velocity dependency on length and this species and instrument dependent property is also influenced by knottiness. This research is dealing with time-lag determination by different sensor positioning in situ ToF measurements. ToF longitudinal measurements were conducted on 120 90 mm×140 mm specimens of the coniferous species radiata pine, Scots pine, laricio pine and maritime pine. The following commercially available acoustic devices were used: Sylvatest Duo, USLab, and Microsecond Timer. The sensors were arranged for the measurement types “end-to-end”, “on the same surface” and “on opposite surfaces”. ToF data were obtained from the full-length (4 m) specimens and then from the same specimens shortened to 3 m, 2 m and 1 m in length. The in situ procedures of ToF are applicable for a reliable length determination independently from the time-lag (tL) and velocity. The differences observed by end-to-end measurements, with respect to velocity, are below 4.4%. A velocity correction factor can be deduced for each instrument, which is independent of species.

A study on the kinetics and thermal properties of polystyrene/diatomite nanocomposites prepared via in situ ATRP

2018 ◽  
Vol 33 (2) ◽  
pp. 180-197 ◽  
Author(s):  
Khezrollah Khezri ◽  
Yousef Fazli
Keyword(s):  
Molecular Weight ◽  
In Situ Polymerization ◽  
Structural Characteristics ◽  
Nitrogen Adsorption ◽  
Linear Increase ◽  
Size Exclusion ◽  
Scanning Calorimetry ◽  
Morphological Studies ◽  
Exclusion Chromatography

Pristine mesoporous diatomite was employed to prepare polystyrene/diatomite composites. Diatomite platelets were used for in situ polymerization of styrene by atom transfer radical polymerization to synthesize tailor-made polystyrene nanocomposites. X-Ray fluorescence spectrometer analysis and thermogravimetric analysis (TGA) were employed for evaluating some inherent properties of pristine diatomite platelets. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the diatomite platelets. Evaluation of pore size distribution and morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography, respectively. Linear increase of ln ( M0/M) with time for all the samples shows that polymerization proceeds in a living manner. Addition of 3 wt% pristine mesoporous diatomite leads to an increase of conversion from 72% to 89%. Molecular weight of polystyrene chains increases from 11,326 g mol−1 to 14134 g mol−1 with the addition of 3 wt% pristine mesoporous diatomite; however, polydispersity index values increases from 1.13 to 1.38. Increasing thermal stability of the nanocomposites is demonstrated by TGA. Differential scanning calorimetry shows an increase in glass transition temperature from 81.9°C to 87.1°C by adding 3 wt% of mesoporous diatomite platelets.

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