Improved X-ray Spectrum Simulation for Electron Microprobe Analysis

The accurate calculation of characteristic peak intensity is essential for interpreting X-ray spectra in electron microprobe analysis. Conventionally, the measured intensity from a standard of known composition is used as a reference to simplify the calculation. However, if no such standard is available, then all factors influencing X-ray generation and X-ray detection efficiency must be included. If the intensity and energy distribution of the background radiation can also be calculated, the investigator can simulate an entire spectrum from an assumed composition, gaining powerful benefits in setting up an experiment and in confirming the results. The study presented here demonstrates a fast method of spectrum simulation, suitable for energy-dispersive spectroscopy (EDS), and assesses the accuracy using 309 spectra from samples of known composition. These include K, L, and M lines from elements of atomic number 6-92, excited by beam energies in the range of 5-30 keV. The RMS error between 360 measured and calculated peak intensities was found to be 7.1%. Central to the method is the use of the ratio of peak intensity/total background intensity, which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions.

In high-throughput proteomics the development of computational methods and novel experimental strategies often rely on each other. In certain areas, mass spectrometry methods for data acquisition are ahead of computational methods to interpret the resulting tandem mass spectra. Particularly, although there are numerous situations in which a mixture tandem mass spectrum can contain fragment ions from two or more peptides, nearly all database search tools still make the assumption that each tandem mass spectrum comes from one peptide. Common examples include mixture spectra from co-eluting peptides in complex samples, spectra generated from data-independent acquisition methods, and spectra from peptides with complex post-translational modifications. We propose a new database search tool (MixDB) that is able to identify mixture tandem mass spectra from more than one peptide. We show that peptides can be reliably identified with up to 95% accuracy from mixture spectra while considering only a 0.01% of all possible peptide pairs (four orders of magnitude speedup). Comparison with current database search methods indicates that our approach has better or comparable sensitivity and precision at identifying single-peptide spectra while simultaneously being able to identify 38% more peptides from mixture spectra at significantly higher precision.

A Monte Carlo simulation code has been developed to describe the x-ray generation in a specimen for electron probe microanalysis (EPMA), enabling x-ray spectra observed by EPMA to be reproduced theoretically. The Monte Carlo simulation is based on the use of the Mott cross section and Bethe stopping power equation in describing elastic and inelastic scattering processes, respectively. With respect to x-ray generation the Sommerfeld theory for bremsstrahlung radiation was described by equations of Kirkpatrick–Wiedmann and of Statham for bremsstrahlung cross section. The up-to-date compilation of mass absorption coefficient by Henke, Gullikson, and Davis [At. Data Nucl. Data Tables 54, 181 (1993)] is used to evaluate attenuation of x-ray intensity. To verify the present Monte Carlo simulation measurements of x-ray spectra for Cu and Rh targets have been performed for primary electron energies of 10–30 keV by energy-dispersive x-ray spectrometry of an electron probe microanalyzer. Excellent agreement between experimental spectra and calculated results has been confirmed in the cases investigated, leading to the conclusion that the Monte Carlo simulation technique will be a powerful tool for more comprehensive understanding of x-ray generation in EPMA specimens.

Castaing’s first electron probe microanalyzer(l) was a modified electrostatic transmission electron microscope equipped with a curved-crystal x-ray spectrometer. This combination was perfected in later years by the introduction of Langmuir-Blodgett devices(2) and of diffractors consisting of evaporated metal layers, (3) so that the elements of atomic number above 3 could also be observed and analyzed.

This study details a one-time ray-tracing optimization method for the optimization of LED illumination systems [S.-C. Chu and H.-L. Yang, "One-time ray-tracing method for the optimization of illumination system," in Proceedings of International Conference on Optics in Precision Engineering and Nanotechnology (icOPEN, 2013), 87692M]. This method optimizes the performance of illumination systems by modifying the light source's radiant intensity distribution with a freeform lens, instead of modifying the illumination system structure. Because illumination system structures are unchanged in the design process, a designer can avoid the common problems faced when designing illumination systems, i.e., the repeated and time-consuming ray-tracing process when optimizing the illumination system parameters. The easy approaches of the proposed optimization method to sample the target illumination areas and to divide the light source radiant intensity distribution make the proposed method can be applied to both direct-lit and non-direct-lit illumination systems. To demonstrate the proposed method, this study designs an illuminator for a tube photo-bioreactor using the proposed one-time ray-tracing method. A comparison shows that in the designing of the photo-bioreactor, tracing all rays one time requires about 13 hours, while optimizing the light source's radiant intensity distribution requires only about twenty minutes. The considerable reduction in the ray-tracing time shows that the proposed method is a fast and effective way to design illumination systems.

A mathematical model for the radiation intensity distribution of carbon fiber electric heating radiator is set up,the radiation intensity distribution of different kind of carbon fiber electric heating elements is simulated with software MATLAB,and the characteristic of its space radiation is dis-cussed.The simulating results show that the radiation intensity distribution of the carbon fiber electric heating elements is greatly affected by its structure parameters,with the changing of radius,there is an optimum value about the space radiation intensity,the non-uniformity of radiation intensity distribution increases with the increasing of radius.Compared with the characteristic of radiation intensity distribution of different kinds of electric heating elements,the radiation intensity dis-tribution fields of same specification electric heating elements are basically consistent,but the radiation intensity values change with the type of elements.The radiation intensity of carbon fiber electric heating element is significantly higher than common metal heating element,which can be significantly improved by painting with two sides infrared coating.By ad-justing the formulae of coating,infrared radiation spectrum distribution can be changed in order to satisfy the special heat-ing requirements.The experiment results show that model test data is approximately accordance with simulating result,which supplies a design reference to carbon fiber heating radiation field in the future.

Elemental mapping at the microstructural level by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), while widely applied in science, engineering, and technology, has been limited in performance by the throughput of the lithium-drifted silicon detector [Si(Li)-EDS] which restricts the number of X-ray counts measured per image pixel. The emergence of the silicon drift detector (SDD-EDS) has greatly extended the X-ray throughput, by a factor of 25 to 70 for the same spectral resolution. This improved performance enables practical X-ray spectrum imaging (XSI), in which a complete X-ray spectrum is recorded at each image pixel. By performing complete quantitative corrections for background, peak overlap, and matrix effects to each pixel spectrum, full compositional mapping can be achieved. Various elemental mapping collection strategies are described, including quantitative mapping at the major (concentration C > 0.1 mass fraction), minor (0.01 ≤ C ≤ 0.1), and trace (C < 0.01) constituent levels, extreme pixel density (gigapixel) mapping, rapid mapping (in 10 seconds or less), and high spatial resolution mapping with the thermal field emission gun scanning electron microscope.

A computer model that takes into account the effect of aerodynamic and solar heating, sky irradiation, and radiative cooling on infrared emission from missile noses is presented. The heat transfer equation was solved with numerical techniques both in the steady-state (constant speed and altitude flight of cruise missiles) and in the nonstationary regime (quickly variable speed and altitude of short to medium range ballistic missiles) to give the temperature distribution on the skin surface. The corresponding head-on absolute infrared emission in the 3 to 5 pm and 8 to 12 jim spectral bands was computed as a function of time of flight and missile altitude. Results show a strong dependence of temperature and radiant intensity distributions on thermal and geometrical properties of the skin material, on the character of the aerodynamic flow (laminar or turbulent boundary layer), and on the physical characteristics of the atmosphere. By varying these parameters into reasonable ranges, infrared emissions spanning over more than an order of magnitude were obtained. The comparison with data corresponding to a skin uniformly kept at the boundary layer effective temperature showed that huge overestimates of the infrared emission can be found when the target is flying at high speed and high altitude. By computing the ratio of the in-band total radiant intensity in the 3 to 5 p.m and 8 to 12 p.m spectral regions, the relative merits of these regions for the detection of a given target are given as a function of missile altitude.

Transthyretin is a tetrameric protein associated with the commonest form of systemic amyloid disease. Using isotopically labeled proteins and mass spectrometry, we compared subunit exchange in wild-type transthyretin with that of the variant associated with the most aggressive form of the disease, L55P. Wild-type subunit exchange occurs via both monomers and dimers, whereas exchange via dimers is the dominant mechanism for the L55P variant. Because patients with the L55P mutation are heterozygous, expressing both proteins simultaneously, we also analyzed the subunit exchange reaction between wild-type and L55P tetramers. We found that hybrid tetramers containing two or three L55P subunits dominate in the early stages of the reaction. Surprisingly, we also found that, in the presence of L55P transthyretin, the rate of dissociation of wild-type transthyretin is increased. This implies interactions between the two proteins that accelerate the formation of hybrid tetramers, a result with important implications for transthyretin amyloidosis.

ABSTRACTBulk samples of a novel cermet (ceramic/metal composite) hydrogen transport membrane (HTM) were subjected to thermal cycling in the temperature range between 25-850°C to study phase transformations and microstructural changes under thermal shock. Scanning electron microscopy (SEM) and electron probe micro analyzer (EPMA) with energy dispersive spectroscopy (EDS) were used to characterize the microstructural and chemical changes in the membrane upon thermal cycling. SEM &amp; EPMA analyses indicated that the temperature gradient during thermal cycling produced more micro-cracks inside the HTM disc, whereas, the chemical reaction between Pd and oxygen to form PdO disturbed the continuity of the metal palladium (Pd) - Yttria Stabilized Zirconia (YSZ) dual phases interconnection system from surface down. The agglomerates of un-crystallized YSZ grains found to be the inherent in the cracks of the as-received HTM. A combination of trans-granular and inter-granular crack propagation results around the YSZ grains and the new precipitates. Based on the electron fractography analyses by both SEM and EPMA, the micro voids coalescence develops ahead of the crack tips in the cross-section of the HTM after 500 thermal cycles.

Dolomite [CaMg(CO3)2] is an important carbonate mineral mainly composed of calcium magnesium carbonate. The correct determination of magnesium content in carbonate rocks is important for accessing its suitability for different applications; however, presence of different phases with varying magnesium contents makes their analysis difficult. In the present work, a natural carbonate mineral dolomite is analyzed qualitatively and quantitatively using laser-induced breakdown spectroscopy along with X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy and electron-probe microanalysis. The optical emission spectra recorded in 200–720 nm wavelength region revealed presence of emission lines for Ca, Mg, Al, Sr, and Na with varying intensities. We used two different techniques, that is, Boltzmann plot and Saha–Boltzmann plot methods to calculate the plasma temperature, and an average value of 4500 ± 450 K was deduced.The Stark broadening line profile method was exploited to calculate the electron number density using calcium and magnesium lines which resulted in 2.39 × 1017 cm–3. The quantitative compositional analysis was carried out using calibration-free laser-induced breakdown spectroscopy method for which the local thermodynamic equilibrium and optically thin plasma conditions were satisfied.The composition for dolomite major constituents calcium and magnesium were estimated as 68.58 and 31.41%, respectively.The results demonstrated the LIBS, EDS, and EPMA ability as an effective, powerful and complementary analytical techniques for the elemental composition analysis of carbonate minerals.

More and more lighting applications require the design of dedicated optics to achieve a given radiant intensity or irradiance distribution. Freeform optics has the advantage of providing such a functionality with a compact design. It was previously demonstrated in [Bäuerle et al., Opt. Exp. 20, 14477-14485 (2012)] that the up-front computation of the light path through the optical system (ray mapping) provides a satisfactory approximation to the problem, and allows the design of multiple freeform surfaces in transmission or in reflection. This article presents one natural extension of this work by introducing an efficient optimization procedure based on the physics of the system. The procedure allows the design of multiple freeform surfaces and can render high resolution irradiance patterns, as demonstrated by several examples, in particular by a lens made of two freeform surfaces projecting a high resolution logo (530 × 160 pixels).

In present work, the aerodynamic characteristics and the infrared radiation (IR) features of the spherical convergent flap nozzle (SCFN) under vector actuating operations have been studied numerically. The infrared radiation (IR) features of the nozzle under different vector actuation angle have been studied using the reverse Monte-Carlo method (RMCM). Several parameters, such as IR intensity, radiation brightness, and the spectral radiant intensity of the nozzle, are analyzed in detail. The results show that SCFN radiation intensity distribution gradually transitions from two-peak distribution to single-peak distribution. When the pitching motion is activated, the “second peak” located downstream of the deflection vector angle is gradually weakened and disappears. The peak gradually approaches the peak of the mixer, and the contribution of the mixer gradually dominates. With the increase of geometric vector angle in the pitching direction, the detection angle of the nozzle’s infrared radiation intensity peak is less than the geometric vector angle, meanwhile the decrease of the peak value of the infrared radiation intensity of the nozzle is parabolic with the geometric vector angle. Along the direction of the pitching operation, the average value of the infrared radiation at a detection angle of −35° to 35° decreases linearly. When the yaw motion is activated, the infrared radiation intensity distribution in the backward direction of the nozzle exhibits a single-peak feature, and the detection angle at which the peak is located is also smaller than its geometric vector angle. Using the detection angle of the peak as the axis of symmetry, the curve of the infrared radiation intensity distribution behind the nozzle is symmetrical. As the geometric vector angle in the yaw direction increases, along the direction of the pitching operation, both the average value of infrared radiation at a detection angle of -35° to 35° and the peak value of the backward infrared integrated radiation intensity of the nozzle decrease linearly. Besides, the maximum drop is much smaller than the maximum drop during pitching operation.

Software for simulation of different characteristic of spontaneous electromagnetic radiation, generated by a relativistic electron beam in external magnetic field, is presented. It consists of several different computer codes, which are in consistent with each other. Computer codes calculate spatial and spectral distributions of electromagnetic radiation intensities. Explicit expressions are used for the emitted electric field components, including the so-called velocity term. The codes simulate the electron trajectory in the external magnetic field numerically, by using the experimentally measured values of the field. The real geometry is used for the simulation. For example, the near-field effects are taken into account. The electron beam emittance is simulated by numerical convolution of the Gaussian electron distribution in a beam with the spatial distribution of the electromagnetic radiation, generated by one electron. As an example, the edge radiation, generated at the ends of bending magnets of the Siberia-2 storage ring, is considered. Calculations show that the edge radiation intensity must significantly exceed the intensity of standard synchrotron radiation, formed by the homogeneous field of a bending magnet, in the infrared and ultraviolet spectral regions. This set of computer codes will also find wide application in the new project of the fourth generation of a specialized synchrotron radiation source ISSI-4.

The necessary, estimates were obtained and it was demonstrated experimentally that the Bragg diffraction of light by ultrasonic waves in air may be used to measure the intensity distribution of laser radiation. A transducer utilizing an X-cut quartz crystal was developed to implement this technique. Measurements were made of the angular distribution of the ultrasonic field and its divergence was determined as 4×10–3 rad at 0.9 MHz. In order to confirm this possibility, measurements were made of the laser radiation distribution at λ = 0.6328 μ in the incident and Bragg-diffracted radiation.