scholarly journals Molecular structure retrieval directly from laboratory-frame photoelectron spectra in laser-induced electron diffraction

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Sanchez ◽  
K. Amini ◽  
S.-J. Wang ◽  
T. Steinle ◽  
B. Belsa ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
A Priori ◽  
Carbonyl Sulfide ◽  
Bond Distance ◽  
Laboratory Frame ◽  
Photoelectron Spectra ◽  
Molecular Scattering ◽  
Retrieval Method ◽  
Temporal Precision ◽  
Scattering Signal

AbstractUbiquitous to most molecular scattering methods is the challenge to retrieve bond distance and angle from the scattering signals since this requires convergence of pattern matching algorithms or fitting methods. This problem is typically exacerbated when imaging larger molecules or for dynamic systems with little a priori knowledge. Here, we employ laser-induced electron diffraction (LIED) which is a powerful means to determine the precise atomic configuration of an isolated gas-phase molecule with picometre spatial and attosecond temporal precision. We introduce a simple molecular retrieval method, which is based only on the identification of critical points in the oscillating molecular interference scattering signal that is extracted directly from the laboratory-frame photoelectron spectrum. The method is compared with a Fourier-based retrieval method, and we show that both methods correctly retrieve the asymmetrically stretched and bent field-dressed configuration of the asymmetric top molecule carbonyl sulfide (OCS), which is confirmed by our quantum-classical calculations.

scholarly journals Network structure and thermal properties of bioactive (SiO2–CaO–Na2O–P2O5) glasses

2019 ◽  
Vol 55 (6) ◽  
pp. 2303-2320
Author(s):  
M. Fábián ◽  
Zs. Kovács ◽  
J. L. Lábár ◽  
A. Sulyok ◽  
Z. E. Horváth ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Network Structure ◽  
Photoelectron Spectroscopy ◽  
Function Analysis ◽  
Bond Distance ◽  
High Resolution Electron Microscopy ◽  
Linear Increase ◽  
Electron Diffraction Data ◽  
Bioactive Glasses

AbstractCa- and P-based bioactive glasses are excellent candidates for design and manufacture of biomaterials. Understanding the structure and physico-chemical–thermal behaviour of bioactive glasses is a fundamental step towards the design of a new generation of biocompatible materials. In this study, the structure of SiO2–CaO–Na2O glasses and its derivatives, obtained by substituting Na2O with P2O5 and prepared by melt–quench technique, was studied with neutron and electron diffraction techniques combined with thermal analysis, high-resolution electron microscopy and X-ray photoelectron spectroscopy. Neutron and electron diffraction data were analysed with reverse Monte Carlo simulation and pair distribution function analysis, respectively. Bioactivity of P2O5 substituted glasses was also investigated and proven in vitro using simulated body fluid. Based on the structural analysis, it was found that Si and P atoms are in well-defined tetrahedral units with a bond distance of 1.60 Å for both Si–O and P–O bonds, although P exhibits a higher average coordination number than Si. With increasing phosphate content, tendentious changes in the glass behaviour were observed. Linear increase in Tg, supported by the changes in the average coordination numbers of Si and P, indicates strengthening of network structure with increasing P content and formation of P–O–Ca atomic linkages, which lead to Ca–P-rich atomic environments in the silicate network. These Ca–P-rich environments trap volatile elements and thus decrease the total weight loss during heating at higher P concentrations. In the case of the highest investigated P2O5 content (5 mol%), nanoscale structural inhomogeneity and the formation of Ca–P-rich clusters were also revealed by electron diffraction and atomic resolution imaging. This type of Ca–(Na)–P clustering has a key role in the behaviour of phosphate-substituted silicate glasses under physiological conditions.

Quantifying Neurotransmission Reliability Through Metrics-Based Information Analysis

2011 ◽  
Vol 23 (4) ◽  
pp. 852-881 ◽  
Author(s):  
Romain Brasselet ◽  
Roland S. Johansson ◽  
Angelo Arleo
Keyword(s):  
Spike Train ◽  
Information Transfer ◽  
A Priori ◽  
Similarity Measures ◽  
Conditional Entropy ◽  
Neural Population ◽  
Information Analysis ◽  
Full Account ◽  
Temporal Precision ◽  
Large Spike

We set forth an information-theoretical measure to quantify neurotransmission reliability while taking into full account the metrical properties of the spike train space. This parametric information analysis relies on similarity measures induced by the metrical relations between neural responses as spikes flow in. Thus, in order to assess the entropy, the conditional entropy, and the overall information transfer, this method does not require any a priori decoding algorithm to partition the space into equivalence classes. It therefore allows the optimal parameters of a class of distances to be determined with respect to information transmission. To validate the proposed information-theoretical approach, we study precise temporal decoding of human somatosensory signals recorded using microneurography experiments. For this analysis, we employ a similarity measure based on the Victor-Purpura spike train metrics. We show that with appropriate parameters of this distance, the relative spike times of the mechanoreceptors’ responses convey enough information to perform optimal discrimination—defined as maximum metrical information and zero conditional entropy—of 81 distinct stimuli within 40 ms of the first afferent spike. The proposed information-theoretical measure proves to be a suitable generalization of Shannon mutual information in order to consider the metrics of temporal codes explicitly. It allows neurotransmission reliability to be assessed in the presence of large spike train spaces (e.g., neural population codes) with high temporal precision.

scholarly journals The Community Cloud retrieval for CLimate (CC4CL). Part II: The optimal estimation approach

2017 ◽  
Author(s):  
Gregory R. McGarragh ◽  
Caroline A. Poulsen ◽  
Gareth E. Thomas ◽  
Adam C. Povey ◽  
Oliver Sus ◽  
...  
Keyword(s):  
A Priori ◽  
Optimal Estimation ◽  
Forward Model ◽  
Inversion Method ◽  
Surface Model ◽  
Linear Inversion ◽  
Retrieval Method ◽  
Ice Cloud ◽  
Cloud Models ◽  
Community Cloud

Abstract. The Community Cloud retrieval for Climate (CC4CL) is a cloud property retrieval system for satellite-based multispectral imagers and is an important component of the Cloud Climate Change Initiative (Cloud_cci) project. In this paper we discuss the optimal estimation retrieval of cloud optical thickness, effective radius and cloud top pressure based on the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm. Key to this method is the forward model which, includes the clear-sky model, the liquid water and ice cloud models, the surface model including a bidirectional reflectance distribution function (BRDF), the "fast" radiative transfer solution (which includes a multiple scattering treatment) All of these components and their assumptions and limitations will be discussed in detail. The forward model provides the accuracy appropriate for our retrieval method. The errors are comparable to the instrument noise for cloud optical thicknesses greater than 10. At optical thicknesses less than 10 modelling errors become more significant. The retrieval method is then presented describing optimal estimation in general, the non-linear inversion method employed, measurement and a priori inputs, the propagation of input uncertainties and the calculation of subsidiary quantities that are derived from the retrieval results. An evaluation of the retrieval was performed using measurements simulated with noise levels appropriate for the MODIS instrument. Results show errors less than 10 % for cloud optical thicknesses greater than 10. Results for clouds of optical thicknesses less than 10 have errors ranging up to 20 %.

Elektronenbeugungsmessungen zur Struktur des Methoximethylphosphorylfluorids / Electron Diffraction Investigations of the Structure of Methoxi-methyl-phosphoryl-fluoride

1973 ◽  
Vol 28 (10) ◽  
pp. 1717-1720 ◽  
Author(s):  
Werner Zeil ◽  
Helmuth Kratz ◽  
Joachim Haase ◽  
Heinz Oberhammer
Keyword(s):  
Electron Diffraction ◽  
Bond Distance ◽  
A Value

The structure of Methoxi-methyl-phosphoryl-fluoride has been investigated by electron diffraction on gases. The bond distance of the P-F bond (1.536 Å) corresponds with the value given by Kuchitsu for OPF3 (1.523 ±0.003 Å). The P = O distance is remarkable longer than the value given by Kuchitsu, but corresponds to a value given by Oberhammer for the molecule OP (OCH3)3.

scholarly journals Electron Diffraction Based Analysis of Phase Fractions and Texture in Nanocrystalline Thin Films, Part III: Application Examples

2012 ◽  
Vol 18 (2) ◽  
pp. 406-420 ◽  
Author(s):  
J.L. Lábár ◽  
M. Adamik ◽  
B.P. Barna ◽  
Zs. Czigány ◽  
Zs. Fogarassy ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Computer Program ◽  
Phase Analysis ◽  
A Priori ◽  
Fiber Texture ◽  
Quantitative Phase Analysis ◽  
Volume Fractions ◽  
Selected Area Electron Diffraction ◽  
Current Implementation ◽  
Downhill Simplex

AbstractIn this series of articles, a method is presented that performs (semi)quantitative phase analysis for nanocrystalline transmission electron microscope samples from selected area electron diffraction (SAED) patterns. Volume fractions and degree of fiber texture are determined for the nanocrystalline components. The effect of the amorphous component is minimized by empirical background interpolation. First, the two-dimensional SAED pattern is converted into a one-dimensional distribution similar to X-ray diffraction. Volume fractions of the nanocrystalline components are determined by fitting the spectral components, calculated for the previously identified phases with a priori known structures. These Markers are calculated not only for kinematic conditions, but the Blackwell correction is also applied to take into account dynamic effects for medium thicknesses. Peak shapes and experimental parameters (camera length, etc.) are refined during the fitting iterations. Parameter space is explored with the help of the Downhill-SIMPLEX. The method is implemented in a computer program that runs under the Windows operating system. Part I presented the principles, while part II elaborated current implementation. The present part III demonstrates the usage and efficiency of the computer program by numerous examples. The suggested experimental protocol should be of benefit in experiments aimed at phase analysis using electron diffraction methods.

Relationship Between Radiation Stability and Molecular Structure of Nitramine Explosives

1992 ◽  
Vol 296 ◽  
Author(s):  
James J. Pinto
Keyword(s):  
Molecular Structure ◽  
Binding Energy ◽  
Mass Spectra ◽  
Bond Distance ◽  
Radiation Stability ◽  
Photoelectron Spectra ◽  
X Rays ◽  
First Order ◽  
First Order Kinetics ◽  
Cyclotrimethylene Trinitramine

AbstractThe radiation stabilities of the nitramine explosives 1,4-dinitroglycolurile (DINGU), 1,4-dimethyl-2,5-dinitroglycolurile (DMD) and hexanitrohexaazaisowurtzitane (HNIW) have been determined using XPS. Samples were exposed to x-rays for times up to eight hours while photoelectron spectra were recorded in the carbon, oxygen, and nitrogen Is energy regions and mass spectra were recorded of gases evolved during the decomposition process. These data are compared to the previously determined stabilities for cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HlMX). The N1s spectra of the irradiated materials show the NO2 peak decreases relative to the total nitrogen signal while low binding energy peaks grow. The rate of loss of the NO2 peak was fit to first order kinetics and the rate constants obtained show some correlation with the N-N bond strength as measured by the average N-N bond distance and the average NO2 asymetric stretch frequency. Despite the differences in structure of these molecules (DINGU and DMD are bicyclic rings, RDX and HMX are rings and HNIW is a cage) the radiation stability appears to be controlled by the strength of the N-N bond.

Measuring Electrostatic Potential Profiles across Amorphous Intergranular Films by Electron Diffraction

2005 ◽  
Vol 12 (2) ◽  
pp. 160-169 ◽  
Author(s):  
Christoph T. Koch ◽  
Somnath Bhattacharyya ◽  
Manfred Rühle ◽  
Raphaëlle L. Satet ◽  
Michael J. Hoffmann
Keyword(s):  
Electron Diffraction ◽  
Laboratory Frame ◽  
Potential Profile ◽  
Specimen Thickness ◽  
One Dimensional ◽  
Intergranular Films ◽  
Transmission Electron ◽  
Specimen Orientation ◽  
Diffraction Patterns ◽  
The One

Amorphous 1–2-nm-wide intergranular films in ceramics dictate many of their properties. The detailed investigation of structure and chemistry of these films pushes the limits of today's transmission electron microscopy. We report on the reconstruction of the one-dimensional potential profile across the film from an experimentally acquired tilt series of energy-filtered electron diffraction patterns. Along with the potential profile, the specimen thickness, film orientation with respect to the grain lattice and specimen surface, and the absolute specimen orientation with respect to the laboratory frame of reference are retrieved.

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