Intermediate Spectra Research Articles

Spectral features of the wake and power fluctuations of model wind turbines under low-level jets

Laboratory experiments are conducted to inspect the modulation of model low-level-jet (LLJ) velocity profiles on the wake of a model wind turbine and power output fluctuations and a spectral structure of a simple two-turbine system in an aligned configuration. The scenario with a canonical incoming turbulent boundary layer profile is included for comparison. The results reveal a significant effect of the relative height of the LLJ peak velocity on the near and intermediate wake and power output fluctuations. Those effects are more notorious with the LLJ peak velocity coincident with the turbine top tip. The strong mean shear right above the wake promotes enhanced vertical transport and generation of energetic coherent motions. In particular, the near and intermediate wake velocity spectra showed a robust local signature with a streamwise length on the order of ∼4 times the rotor diameter. Although this shear layer did not significantly affect the spectrum of the power output fluctuations, the relatively large-scale velocity fluctuations may affect wind turbines' downwind in arrays.

Metabolomics of Arterial Stiffness.

Arterial stiffness (AS) is one of the earliest detectable signs of structural and functional alterations of the vessel wall and an independent predictor of cardiovascular events and death. The emerging field of metabolomics can be utilized to detect a wide spectrum of intermediates and products of metabolism in body fluids that can be involved in the pathogenesis of AS. Research over the past decade has reinforced this idea by linking AS to circulating acylcarnitines, glycerophospholipids, sphingolipids, and amino acids, among other metabolite species. Some of these metabolites influence AS through traditional cardiovascular risk factors (e.g., high blood pressure, high blood cholesterol, diabetes, smoking), while others seem to act independently through both known and unknown pathophysiological mechanisms. We propose the term ‘arteriometabolomics’ to indicate the research that applies metabolomics methods to study AS. The ‘arteriometabolomics’ approach has the potential to allow more personalized cardiovascular risk stratification, disease monitoring, and treatment selection. One of its major goals is to uncover the causal metabolic pathways of AS. Such pathways could represent valuable treatment targets in vascular ageing.

A novel SN/MOC collaborative method for few-group cross-section generation with versatile neutron spectral adaptability in advanced reactor physics analysis

This study proposes a novel deterministic discrete ordinate method (SN)/method of characteristics (MOC) collaborative method for few-group cross-section generation to realize versatile spectral computation for different types of neutron energy spectra. The method encompasses fast/intermediate/thermal spectra, which facilitates advanced reactor physics analysis. The SN with multi-direction scanning was initially used to compute the region-wise isotope-dependent background cross-sections to accommodate the complicated spectral features over the entire energy range and obtain the fine-group cross-sections. The MOC was then adopted to acquire accurate weighting spectra over the entire domain for few-group cross-section generation. As a practical application, the proposed method was implemented in AVENUE code development, which was employed for the reactor physics analysis of typical fast/thermal spectra, over-moderated thermal spectra, and complicated intermediate spectra with additional parallelization and acceleration techniques. The verification results revealed that the proposed SN/MOC collaborative method enables accurate few-group cross-section generation with versatile spectral adaptability.

Temperature effects on calcium binding to caseins

The kinetics of binding of calcium ions in molar excess to individual caseins and casein ingredients was studied in pH 6.4 aqueous solutions using stopped-flow absorption spectroscopy. An initial second-order reaction, faster for β-casein than for αs-casein due to lower energy of activation (ΔEa1,β = 8.2 kJ∙mol−1; ΔEa1,α = 18.1 kJ∙mol−1, respectively), is followed by a slower first-order reaction with similar energies of activation (ΔEa2,β = 25.3 kJ∙mol−1 and ΔEa2,α = 20.7 kJ∙mol−1) as determined from temperature dependence of rate between 25 °C and 50 °C. Sodium caseinate reacts faster with calcium than both αs-casein and β-casein in the first reaction of the two consecutive reactions, while the rate of the second falls between αs-casein and β-casein. Global spectral analysis showed the UV–visible spectra of the reaction intermediates of the caseins to be more similar to the final products than to the initial casein reactants. Dynamic and static light scattering indicated decreasing particle sizes and increasing particle surface upon calcium-binding most significantly at low temperatures. The calcium binding to casein was found endothermic by isothermal titration calorimetry. Calcium binding seems to be controlled by enthalpy/entropy compensation corresponding to an isoequilibrium temperature of 38 °C in agreement with binding of calcium to o-phosphoserine rather than to aspartate or glutamate side chains of the caseins. Binding capacity and affinity for calcium to αs-casein and sodium caseinate both increased with increasing temperature in agreement with the endothermic nature of the binding. Decreasing enthalpy of binding for each calcium indicating a decrease in heat capacity of the caseins upon calcium-binding. The small difference between binding enthalpy and energy of activation for association of calcium to αs-casein lead to the conclusion that calcium dissociation goes through an early transition state. The rate of calcium dissociation hardly depends on temperature also explaining why calcium binding to caseins is important for calcium bioaccessibility.

Spin liquid to spin glass crossover in the random quantum Heisenberg magnet

We study quantum SU($M$) spins with all-to-all and random Heisenberg exchange interactions of root-mean-square strength $J$. The $M \rightarrow \infty$ model has a spin liquid ground state with the spinons obeying the equations of the Sachdev-Ye-Kitaev (SYK) model. Numerical studies of the SU(2) model with $S=1/2$ spins show spin glass order in the ground state, but also display SYK spin liquid behavior in the intermediate frequency spin spectrum. We employ a $1/M$ expansion to describe the crossover from fractionalized fermionic spinons to a confining spin glass state with weak spin glass order $q_{EA}$. The SYK spin liquid behavior persists down to a frequency $\omega_\ast \sim J q_{EA}$, and for $\omega < \omega_\ast$, the spectral density is linear in $\omega$, thus quenching the extensive zero temperature entropy of the spin liquid. The linear $\omega$ spectrum is qualitatively similar to that obtained earlier using bosonic spinons for large $q_{EA}$. We argue that the extensive SYK spin liquid entropy is transformed as $T \rightarrow 0$ to an extensive complexity of the spin glass state.

Structural, elastic, mechanical, electronic, magnetic and optical properties of half-Heusler compounds CoFeZ (Z = P, As, Sb): A GGA+U approximation

The first-principles study technique is implemented to explore Co-based H–H compounds, namely CoFeP, CoFeAs, and CoFeSb. In this study we have investigated the structural, elastic, electronic, magnetic, and optical properties using DFT as a fundamental approach within simulation package WIEN2k, utilizing linearized augmented plane wave method with full potential. Calculations for electronic exchange–correlation energy are performed using GGA (Generalized Gradient Approximation) approach together with the on-site Coulomb interactions effect as (GGA + U). Using Phono3py code, we have calculated the phonon spectrum of CoFeZ compounds and there is no negative frequency in the phonon spectrum which shows the dynamic stability of CoFeZ (Z = P, As, Sb) compounds. Large lattice constants are seen for all three compounds CoFeP, CoFeAs, and CoFeSb. Elastically, the former two compounds CoFeP and CoFeAs are ductile while the latter one, CoFeSb is brittle. All the compounds show small band gaps for spin-down channels hence confirming half-metallic character. It is found that magnetic moments follow the Slater–Pauling 18Mt=Zt-18 electron rule with the high total magnetic moments. Also, optical properties such as refractive index, absorption coefficient, dielectric function, conductivity, and reflectivity are calculated and discussed, which show that all the compounds are highly active at intermediate energy spectra.

Recurring Nova RS Oph spectroscopic observation at Bosscha Observatory and ITERA Astronomical Observatory (IAO)

We report low and intermediate resolution spectra of the recurrent nova RS Oph taken at two observatories. A low resolution spectrum (R ≈ 1000) was taken at ITERA Astronomical Observatory (IAO) in Lampung by using 25 cm (f/8) RC Astrograph telescope equipped with a LISA Pack Spectrograph eight days after the outburst. Twenty intermediate spectra (R ≈ 5000) were taken on several consecutive nights using LHIRES III spectrograph attached to a 25 cm (f/10) Meade LX-200R telescope at Bosscha Observatory, Lembang. We identified significant change in the strength of atomic lines from low resolution spectrum compared to previous observations. A clear and distinct Balmer emission decrement can be seen from the spectrum. Our intermediate resolution spectroscopy revealed a variability of P-Cygni profile on a broad Hα line. The P-Cygni profile evolved and disappeared at recent observations. It is thought that there was a new shell formed after the outburst and later combined with the previous shell in the next days. From the broad Hα profile, we measured and found decreasement in expansion velocity during our observation. We estimated vexp = 2907.97 ± 64.14 km/s and vexp = 997.12 ± 8.18 km/s on 1.6440 and 22.729 days after the outburst, respectively.

2D NMR peak profiling to compare chemical differences between batches of pentosan polysulfate sodium

Pentosan Polysulfate Sodium (PPS) is a semi-synthetic polysulfated xylan sourced from beechwood tree barks. PPS, which is mainly composed of a xylose chain with branched O-methyl-glucuronate (MGA), can have heterogeneity in monosaccharide species, sequence and chemical modifications including sulfation and acetylation. The monosaccharide composition in polysaccharide therapeutics is a frequently quoted quality attribute (QA), which has been assessed using two-dimensional (2D) 1H–13C HSQC NMR. However, the sensitivity of 2D NMR for the assessment of PPS inter-lot variability from the same manufacturer was unclear and questions remained whether 2D NMR had sufficient sensitivity to distinguish normal batch to batch variations in this QA. Here, a 2D peak profile method was applied to compare high-resolution semi-quantitative (semi-q) HSQC spectra with the inclusion of intermediate precision spectra collected on two PPS drug lots released 29 months apart (where one of the lots was expired). The semi-q HSQC NMR confirmed the mass equivalence of total polysaccharides, O-Methyl and acetyl groups between the two lots. The 2D spectral peak profile results readily identified significant lot-to-lot differences (p < 0.05) in relative distribution among most monosaccharide species, in addition to heterogeneity in MGA distribution and acetyl transfer from PPS to free acetate in the expired lot. Precisely measured chemical QAs are prerequisites to establish normal batch variation in the innovator product, providing important reference ranges for complex generic drug developers. Overall, high-resolution semi-q HSQC NMR may provide a sensitive tool to measure fine chemical differences in polysaccharide therapeutics needed to establish chemical QAs and compare batches without concerns of intrinsic NMR method variation.

Bright spectroscopic binaries: II . A study of five systems with orbital periods of days

We present a detailed analysis of five bright spectroscopic binary systems (HD 18665, HD 27131, HD 171852, HD 215550, HD 217427) that have orbital periods of P < 500 days. We determined the complete set of orbital parameters using the toolkit RadVel by analyzing the observed radial velocity curves. To study the properties of the five systems, we also analyzed the intermediate resolution spectra (R = 20,000) observed with the TIGRE telescope and determined the stellar parameters of the primary stars using the toolkit iSpec. With Gaia Early Data Release 3 parallaxes, a correction for interstellar extinction using the 3D dust map, and bolometric corrections, we placed the stars in the Hertzsprung-Russell diagram and compared the positions with stellar evolution tracks calculated with the Eggleton code to determine the masses and ages of the primary stars. They have all evolved to the giant phase. Finally, we were able to determine the masses of the secondary stars and to estimate the orbital inclinations i of the binary systems.

Development of Genistein Synthesis for Use as a Certified Reference Material

Introduction. The use of certified reference materials (CRMs) ensures metrological traceability and comparability of analysis results performed in different laboratories, by different analysts, at different times. Genistein is a promising substance with a wide spectrum of pharmacological action. genistein is widely used in dietary supplements. Development of regulatory documents for CRM of genistein will ensure the quality of drugs and dietary supplements.Aim. Aim of our study is to improve of the ways of synthesis and determination of spectrum characteristics of genistein for the certification of CRM.Materials and methods. We used synthetic genistein, (Ph.D. V. Yu. Kovtun SPC "Pharmzashchita") (sample № 1) and genistein synthesized and studied at the departments of pharmaceutical chemistry and chemical technology of medicinal substances SPCPU (sample № 2). Infrared spectra of genistein samples were collected on an FSM 1201 infrared Fourier spectrometer (OOO Infraspek, Russia) via KBr pellets technique. All the spectra were collected in the 4000–500 cm−1 range. The NMR (1H and 13C) measurements were performed with a BrukerAvance III NMR spectrometer (400 and 100 MHz) (Bruker, Germany) in DMSO-d6 solvent. Raman spectra were recorded by an ORTES-785TRS-2700 analytical Raman scattering system at a laser power of 100 mW (OPTEC JSC, Russia). Laser interaction time was 5, 10, 20 and 60 seconds. The results were processed using the software "BWSpec 4.10_4", USA. GC-MS was performed on an Agilent Technologies 7890A gas chromatograph (Agilent Technologies, USA) with a 7693 autoinjector and a Hewlett Packard 5975C mass selective detector.Results and discussion. The synthesis was carried out according to the developer's method. The stage "removal of the alkyl protection" has been improved. The spectra of the synthesis intermediate of genistein (biochanin A) correspond to the literature data. Samples of genistein were investigated by methods: MC and NMR 13С, 1Н. The structure of the investigated substance was confirmed; Raman and IR spectroscopy showed that the spectra of the samples do not differ from each other and there are no additional signals.Conclusion. The spectrum characteristics of samples of genistein were obtained by NMR, IR and Raman spectroscopy, which will be used in the regulatory documentation for CRM of genistein. All of this will make it possible to control the quality of medicines based on it and to identify substandard dietary supplements.

Sociodemographic and clinical features predictive of SARS-CoV-2 test positivity across healthcare visit-types.

BackgroundDespite increased testing efforts and the deployment of vaccines, COVID-19 cases and death toll continue to rise at record rates. Health systems routinely collect clinical and non-clinical information in electronic health records (EHR), yet little is known about how the minimal or intermediate spectra of EHR data can be leveraged to characterize patient SARS-CoV-2 pretest probability in support of interventional strategies.Methods and findingsWe modeled patient pretest probability for SARS-CoV-2 test positivity and determined which features were contributing to the prediction and relative to patients triaged in inpatient, outpatient, and telehealth/drive-up visit-types. Data from the University of Washington (UW) Medicine Health System, which excluded UW Medicine care providers, included patients predominately residing in the Seattle Puget Sound area, were used to develop a gradient-boosting decision tree (GBDT) model. Patients were included if they had at least one visit prior to initial SARS-CoV-2 RT-PCR testing between January 01, 2020 through August 7, 2020. Model performance assessments used area-under-the-receiver-operating-characteristic (AUROC) and area-under-the-precision-recall (AUPR) curves. Feature performance assessments used SHapley Additive exPlanations (SHAP) values. The generalized pretest probability model using all available features achieved high overall discriminative performance (AUROC, 0.82). Performance among inpatients (AUROC, 0.86) was higher than telehealth/drive-up testing (AUROC, 0.81) or outpatient testing (AUROC, 0.76). The two-week test positivity rate in patient ZIP code was the most informative feature towards test positivity across visit-types. Geographic and sociodemographic factors were more important predictors of SARS-CoV-2 positivity than individual clinical characteristics.ConclusionsRecent geographic and sociodemographic factors, routinely collected in EHR though not routinely considered in clinical care, are the strongest predictors of initial SARS-CoV-2 test result. These findings were consistent across visit types, informing our understanding of individual SARS-CoV-2 risk factors with implications for deployment of testing, outreach, and population-level prevention efforts.

Kinetic Studies of Antioxidant Properties of Ovothiol A.

Ovothiol A (OSH) is one of the strongest natural antioxidants. So far, its presence was found in tissues of marine invertebrates, algae and fish. Due to very low pKa value of the SH group, under physiological conditions, this compound is almost entirely present in chemically active thiolate form and reacts with ROS and radicals significantly faster than other natural thiols. In biological systems, OSH acts in tandem with glutathione GSH, with OSH neutralizing oxidants and GSH maintaining ovothiol in the reduced state. In the present work, we report the rate constants of OSH oxidation by H2O2 and of reduction of oxidized ovothiol OSSO by GSH and we estimate the Arrhenius parameters for these rate constants. The absorption spectra of reaction intermediates, adduct OSSG and sulfenic acid OSOH, were obtained. We also found that OSH effectively quenches the triplet state of kynurenic acid with an almost diffusion-controlled rate constant. This finding indicates that OSH may serve as a good photoprotector to inhibit the deleterious effect of solar UV irradiation; this assumption explains the high concentrations of OSH in the fish lens. The unique antioxidant and photoprotecting properties of OSH open promising perspectives for its use in the treatment of human diseases.

Organelle Genomes and Transcriptomes of Nymphaea Reveal the Interplay between Intron Splicing and RNA Editing.

Posttranscriptional modifications, including intron splicing and RNA editing, are common processes during regulation of gene expression in plant organelle genomes. However, the intermediate products of intron-splicing, and the interplay between intron-splicing and RNA-editing were not well studied. Most organelle transcriptome analyses were based on the Illumina short reads which were unable to capture the full spectrum of transcript intermediates within an organelle. To fully investigate the intermediates during intron splicing and the underlying relationships with RNA editing, we used PacBio DNA-seq and Iso-seq, together with Illumina short reads genome and transcriptome sequencing data to assemble the chloroplast and mitochondrial genomes of Nymphaea ‘Joey Tomocik’ and analyze their posttranscriptional features. With the direct evidence from Iso-seq, multiple intermediates partially or fully intron-spliced were observed, and we also found that both cis- and trans-splicing introns were spliced randomly. Moreover, by using rRNA-depleted and non-Oligo(dT)-enrichment strand-specific RNA-seq data and combining direct SNP-calling and transcript-mapping methods, we identified 98 and 865 RNA-editing sites in the plastome and mitogenome of N. ‘Joey Tomocik’, respectively. The target codon preference, the tendency of increasing protein hydrophobicity, and the bias distribution of editing sites are similar in both organelles, suggesting their common evolutionary origin and shared editing machinery. The distribution of RNA editing sites also implies that the RNA editing sites in the intron and exon regions may splice synchronously, except those exonic sites adjacent to intron which could only be edited after being intron-spliced. Our study provides solid evidence for the multiple intermediates co-existing during intron-splicing and their interplay with RNA editing in organelle genomes of a basal angiosperm.

Mechanism and kinetic study of Paal-Knorr reaction based on in-situ MIR monitoring

An in-depth understanding of reaction processes is beneficial to the development and quality control of chemical products. In this work, the mechanism and kinetics of the Paal-Knorr reaction for pyrrole derivatives are thoroughly studied using in-situ Fourier transform infrared (FTIR) spectroscopy. The hemiacetal amine intermediate, reactants, and products were identified and quantified by the treatment of real-time infrared spectra via chemometrics method and two-dimensional correlation spectroscopy (2DCOS) technique. Based on the IR quantitative models, influences of operating conditions on reaction processes were investigated, and the reaction kinetic model was built with kinetic parameters of two rate-limiting reaction steps calculated. This approach of analysis on the in-situ FTIR data demonstrated the ability to extract useful information on reaction components, especially the intermediate spectrum, from the confounding real-time IR data. The in-situ FTIR monitoring combined with the IR analysis methods is proved as a powerful tool for revealing the reaction mechanism and kinetics.

Blue Light Improves Photosynthetic Performance during Healing and Acclimatization of Grafted Watermelon Seedlings.

To investigate the importance of light on healing and acclimatization, in the present study, grafted watermelon seedlings were exposed to darkness (D) or light, provided by blue (B), red (R), a mixture of R (68%) and B (RB), or white (W; 35% B, 49% intermediate spectra, 16% R) LEDs for 12 days. Survival ratio, root and shoot growth, soluble carbohydrate content, photosynthetic pigments content, and photosynthetic performance were evaluated. Seedling survival was not only strongly limited in D but the survived seedlings had an inferior shoot and root development, reduced chlorophyll content, and attenuated photosynthetic efficiency. RB-exposed seedlings had a less-developed root system. R-exposed seedlings showed leaf epinasty, and had the smallest leaf area, reduced chlorophyll content, and suppressed photosynthetic apparatus performance. The R-exposed seedlings contained the highest amount of soluble carbohydrate and together with D-exposed seedlings the lowest amount of chlorophyll in their scions. B-exposed seedlings showed the highest chlorophyll content and improved overall PSII photosynthetic functioning. W-exposed seedling had the largest leaf area, and closely resembled the photosynthetic properties of RB-exposed seedlings. We assume that, during healing of grafted seedlings monochromatic R light should be avoided. Instead, W and monochromatic B light may be willingly adopted due to their promoting effect on shoot, pigments content, and photosynthetic efficiency.

Spectral and timing evolution of MAXI J1631–479 during the 2018–19 outburst with NICER

ABSTRACT The X-ray transient MAXI J1631–479 went into outburst on 2018 December 21 and remained active for about seven months. Owing to various constraints it was monitored by NICER only during the decay phase of the outburst for about four months. The NICER observations were primarily in the soft state with a brief excursion to the hard intermediate state. While the soft state spectrum was dominated by thermal disc emission, the hard intermediate state spectrum had maximum contribution from the thermal Comptonization. Almost all intermediate-state power spectra had a Type-C low frequency quasi-periodic oscillation (within 4–10 Hz), often accompanied by a harmonic component. The frequency of these oscillations increased and the fractional rms decreased with inner-disc temperature suggesting a geometric origin. The rms spectra during the intermediate state had a hard shape from above 1 keV. Below 1 keV the shape could not be constrained in most cases, while only a few observations showed a rise in amplitude.

A Simple and Efficient Method for Simulating the Electronic Absorption Spectra of Criegee Intermediates: Benchmarking on CH2OO and CH3CHOO.

Criegee intermediates (CIs) play a vital role in the atmosphere-known most prominently for enhancing the oxidizing capacity of the troposphere. Knowledge of their electronic absorption spectra is of vital importance for two reasons: (1) to aid experimentalists in detecting CIs and (2) in deciding if their removal is affected by solar photolysis. In this article we report a simple and efficient method based on the nuclear ensemble method that may be effectively used to compute the electronic absorption spectra of Criegee intermediates without the need for extensive computation of preparing the initial configurations of the starting geometry. We use this method to benchmark several excited-state electronic structure methods and their efficacy in reproducing the electronic absorption spectra of two well-known cases of CI: CH2OO and CH3CHOO. The success and computational feasibility of the methodology are crucial for its applicability to CIs of increasing molecular complexity, which have no known experimentally measured electronic absorption spectra, allowing a guide for experimentalists. Application of the methodology to more complex CIs (e.g., those with extended conjugation or those derived from endocyclic alkenes) will also reveal if solar photolysis becomes a competitive removal process when compared to unimolecular decay or bimolecular chemistry.

Potassium abundances in multiple stellar populations of the globular cluster NGC 4833

NGC 4833 is a metal-poor Galactic globular cluster (GC) whose multiple stellar populations present an extreme chemical composition. The Na-O anti-correlation is quite extended, which is in agreement with the long tail on the blue horizontal branch, and the large star-to-star variations in the [Mg/Fe] ratio span more than 0.5 dex. Recently, significant excesses of Ca and Sc with respect to field stars of a similar metallicity were also found, signaling the production of species forged in H-burning at a very high temperature in the polluters of the first generation in this cluster. Since an enhancement of potassium is also expected under these conditions, we tested this scenario by analysing intermediate resolution spectra of 59 cluster stars including the K I resonance line at 7698.98 Å. We found a wide spread of K abundances, anti-correlated to Mg and O abundances, as previously also observed in NGC 2808. The abundances of K are found to be correlated to those of Na, Ca, and Sc. Overall, this chemical pattern confirms that NGC 4833 is one of the relatively few GCs where the self-enrichment from first generation polluters occurred at such high temperatures that proton-capture reactions were able to proceed up to heavier species such as K and possibly Ca. The spread in K observed in GCs appears to be a function of a linear combination of cluster total luminosity and metallicity, as other chemical signatures of multiple stellar populations in GCs.

The absorption indicatrix as an empirical model to describe anisotropy in X-ray absorption spectra of pyroxenes

AbstractAnisotropic absorption in crystals is routinely observed in many spectroscopic methods and is recognized in visible light optics as pleochroism in crystalline materials. As with other spectrosco-pies, anisotropy in Fe K-edge X-ray absorption spectroscopy (XAS) can serve both as an indicator of the general structural arrangement and as a conundrum in quantifying the proportions of absorbers in crystals. In materials containing multiple absorbers, observed anisotropies can typically be represented by a linear relationship between measured spectroscopic peak intensities and relative absorber concentrations. In this study, oriented XAS analysis of pyroxenes demonstrates that the macroscopic theory that describes visible light absorption anisotropy of triaxially anisotropic materials can also be applied to X-ray absorption in pyroxenes, as long as the orientation and magnitude of the characteristic absorption vectors are known for each energy. Oriented single-crystal XAS analysis of pyroxenes also shows that the measured magnitude of characteristic absorption axes at a given orientation is energy-dependent and cannot be reproduced by linear combination of intermediate spectra. Although the macroscopic model describes a majority of the anisotropy, there is distinct discordance between the observed and interpolated spectra in the pre-edge between 7109 and 7115 eV, which is marked by spikes in RMSE/mean intensity ratio. Absorption indicatrices for samples analyzed in the visible and at X-ray wavelengths are modeled with a three-dimensional (3D) pedal surface, which functions as an empirical way of interpolating between the observed absorption data. This surface only requires a maximum of three coefficients, and results from the summation of 3D lemniscates. An absorption indicatrix model can be used to characterize anisotropic absorption in crystals and provides a way of comparing XAS spectra from randomly oriented crystals, such as those from polished sections, to a database of characterized crystals.

NEUTRON FIELD MOCK-UP DEVELOPMENT FOR THE FLUORIDE SALT REACTORS NEUTRONIC RESEARCH

Experimental work at the LR-0 reactor was carried out to determine the possibility of the mock-up neutron field creation for the fluoride salt-based reactors. Previous calculations and experiments have shown that the fast part of the molten salt reactor (MSR) spectrum is shaped by fluorine and even the Teflon material is suitable for neutronics in that energy range. Properly selected spectrum indices can describe the neutron field of the MSR in fast thermal and intermediate parts of the spectrum. Current research has focused on a deeper study of the possibility of using the filtered thermal and intermediate neutron spectrum of the experimental light water reactor for the physics of fluoride salt-based reactor. LiF-BeF2 (FLIBE) capsule and teflon cylinders are used as a spectrum filters in the LR-0 reactor. Measured results show acceptable C/E-1 agreement in the reaction rates and satisfactory agreement for usage of the FLIBE filtered neutron spectrum determined by the 181Ta(n, γ) monitor as a mock-up in thermal to intermediate energy in the fluoride high-temperature reactor (FHR). Concerning MSR, intermediate spectrum can be reproduced to some extent but not as good as in the case of FHR.