Auswahl der wissenschaftlichen Literatur zum Thema „Spectral overlap integral“

Context. The improvement of large size detectors permitted the development of integral field spectrographs (IFSs) in astronomy. Spectral information for each spatial element of a two-dimensional field of view is obtained thanks to integral field units that spread the spectra on the 2D grid of the sensor. Aims. Here we aim to solve the inherent issues raised by standard data-reduction algorithms based on direct mapping of the 2D + λ data cube: the spectral cross-talk due to the overlap of neighbouring spectra, the spatial correlations of the noise due to the re-interpolation of the cube on a Cartesian grid, and the artefacts due to the influence of defective pixels. Methods. The proposed method, Projection, Interpolation, and Convolution (PIC), is based on an “inverse-problems” approach. By accounting for the overlap of neighbouring spectra as well as the spatial extension in a spectrum of a given wavelength, the model inversion reduces the spectral cross-talk while deconvolving the spectral dispersion. Considered as missing data, defective pixels undetected during the calibration are discarded on-the-fly via a robust penalisation of the data fidelity term. Results. The calibration of the proposed model is presented for the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE). This calibration was applied to extended objects as well as coronagraphic acquisitions dedicated to exoplanet detection or disc imaging. Artefacts due to badly corrected defective pixels or artificial background structures observed in the cube reduced by the SPHERE data reduction pipeline are suppressed while the reconstructed spectra are sharper. This reduces the false detections by the standard exoplanet detection algorithms. Conclusions. These results show the pertinence of the inverse-problems approach to reduce the raw data produced by IFSs and to compensate for some of their imperfections. Our modelling forms an initial building block necessary to develop methods that can reconstruct and/or detect sources directly from the raw data.

The spectral overlap between the emission of a donor molecule and the absorption of an acceptor molecule, quantifiable using the J-integral calculation, is a parameter of extreme importance when studying the excited state energy transfer by either the Főrster or Dexter mechanism. Despite its extreme importance in both mechanisms, it is often misinterpreted, approximated or incorrectly calculated. The calculation of the J-integral is not trivial especially when one wishes to carry out the calculation on measured spectroscopic data. A detailed description for the correct calculation of the J-integral is herein reported and presents a Maple™ assisted template that is capable of performing this calculation in the two different energy scales (nm and cm-1) to yield the value of the J-integral in given units. Specific examples using porphyrin-containing compounds are provided. This Maple™ program is flexible and can be easily adapted to the needs of a researcher. A call for the standardization of the calculation of the J-integral for the facile comparison with other overlap integrals found in the literature is made.

1H-NMR is a very reproducible spectroscopic method and, therefore, a powerful tool for the metabolomic analysis of biological samples. However, due to the high complexity of natural samples, such as plant extracts, the evaluation of spectra is difficult because of signal overlap. The new NMR “Pure Shift” methods improve spectral resolution by suppressing homonuclear coupling and turning multiplets into singlets. The PSYCHE (Pure Shift yielded by Chirp excitation) and the Zangger–Sterk pulse sequence were tested. The parameters of the more suitable PSYCHE experiment were optimized, and the extracts of 21 Hypericum species were measured. Different evaluation criteria were used to compare the suitability of the PSYCHE experiment with conventional 1H-NMR. The relationship between the integral of a signal and the related bin value established by linear regression demonstrates an equal representation of the integrals in binned PSYCHE spectra compared to conventional 1H-NMR. Using multivariate data analysis based on both techniques reveals comparable results. The obtained data demonstrate that Pure Shift spectra can support the evaluation of conventional 1H-NMR experiments.

The Franck–Condon (FC) factor is defined as squares of the Franck–Condon (FC) overlap integral and represents one of the principle fundamental factors of molecular physics. The FC factor is used to determine the transition probabilities in different vibrational levels of the two electronic states and the spectral line intensities of diatomic and polyatomic molecules. In this study, new analytical formulas were derived to calculate Franck–Condon integral (FCI) of harmonic oscillators and matrix elements (xη, e−2cx, and e−cx2) including simple finite summations of binomial coefficients. These formulas are valid for arbitrary values. The results of formulas are in agreement with the results in the literature.

A pair of covalently linked molecular dyads is described in which two disparate boron dipyrromethene dyes are separated by a tolane-like spacer. Efficient electronic energy transfer (EET) occurs across the dyad; the mechanism involves important contributions from both Förster-type coulombic interactions and Dexter-type electron exchange processes. The energy acceptor is equipped with long paraffinic chains that favor aggregation at high concentration or at low temperature. The aggregate displays red-shifted absorption and emission spectral profiles, relative to the monomer, such that EET is less efficient because of a weaker overlap integral. The donor unit is insensitive to applied pressure but this is not so for the acceptor, which has extended π-conjugation associated with appended styryl groups. Here, pressure reduces the effective π-conjugation length, leading to a new absorption band at higher energy. With increasing pressure, the overall EET probability falls but this effect is nonlinear and at modest pressure there is only a small recovery of donor fluorescence. This situation likely arises from compensatory phenomena such as restricted rotation and decreased dipole screening by the solvent. However, the probability of EET falls dramatically over the regime where the π-conjugation length is reduced owing to the presumed conformational exchange. It appears that the pressure-induced conformer is a poor energy acceptor.

AbstractFASTWIND is a unified NLTE atmosphere/spectrum synthesis code originally designed (and frequently used) for the optical/IR spectroscopic analysis of massive stars with winds. Until the previous version (v10), the line transfer for background elements (mostly from the iron-group) was performed in an approximate way, by calculating the individual line-transitions in a single-line Sobolev or comoving frame approach, and by adding up the individual opacities and source functions to quasi-continuum quantities that are used to determine the radiation field for the complete spectrum (see Puls et al. 2005, A&A 435, 669, and updates).We have now updated this approach (v11) and calculate, for all contributing lines (from elements H to Zn), the radiative transfer in the comoving frame, thus also accounting for line-overlap effects in an “exact” way. Related quantities such as temperature, radiative acceleration and formal integral have been improved in parallel. For a typical massive star atmospheric model, the computation times (from scratch, and for a modern desktop computer) are 1.5 h for the atmosphere/NLTE part, and 30 to 45 minutes (when not parallelized) for the formal integral (i.e., SED and normalized flux) in the ranges 900 to 2000 and 3800 to 7000 Å(Δλ = 0.03 Å).We compare our new with analogous results from the alternative code CMFGEN (Hillier & Miller 1998, ApJ 496, 407, and updates), for a grid consisting of 5 O-dwarf and 5 O-supergiant models of different spectral subtype. In most cases, the agreement is very good or even excellent (i.e., for the radiative acceleration), though also certain differences can be spotted. A comparison with results from the previous, approximate method shows equally good agreement, though also here some differences become obvious. Besides the possibility to calculate the (total) radiative acceleration, the new FASTWIND version will allow us to investigate the UV-part of the spectrum in parallel with the optical/IR domain.

We present that the stable and inert Er(III) -encapsulated complexes based on naphthalene and anthracene ligands bearing a Fréchet aryl-ether dendron exhibit much stronger near-IR emission bands bands at 1530 nm, originated from the 4f–4f electronic transition of the first excited state (4 I 13/2) to the ground state (4 I 15/2) of the partially-filled 4f shell. A strong decrease in the fluorescence of G n-aryl ether dendron (n = 0 or 2) is accompanied by strongly increasing the fluorescence intensity of the luminescent anthracene or naphthalene ligand with the generation number of the dendrons. The strong decrease of fluorescence intensity of luminescent ligand such as naphthalene and anthracene units is accompanied by strongly increasing the near infrared (IR) emission of the Er 3+ ions in Er(III) -encapsulated complexes. It could be attributed to the efficient energy transfer process occurring between the aryl-ether dendron and anthracene moiety as well as between dendritic anthracene ligand and Er 3+ ion. Thus, the emission intensity of the lanthanide complexes, upon photoexcitation of aryl-ether dendrons at 290 nm, was dramatically enhanced with an increase in the generation number n of dendrons, due to the site-isolation and light-harvesting effects. In addition, Er 3+-[ G 2- An ]3(terpy) exhibits the stronger PL intensity than Er 3+-[ G 2- Na ]3(terpy)) by 2.5 times, upon photoexcitation of aryl-ether dendrons at 290 nm. It may be due to the fact that the anthracene ligand in Er 3+-[ G 2- An ]3(terpy)) has higher spectral overlap integral (J) value than the naphthalene ligand in Er 3+-[ G 2- Na ]3(terpy) by 1.5 times. Surprisingly, all Er(III) -cored dendrimer complexes have excellent thermal- and photo-stability as well as good solubility.

We analyze two theoretical approaches to ensemble averaging for integrable systems in quantum chaos, spectral averaging (SA) and parametric averaging (PA). For SA, we introduce a new procedure, namely, rescaled spectral averaging (RSA). Unlike traditional SA, it can describe the correlation function of spectral staircase (CFSS) and produce persistent oscillations of the interval level number variance (IV). PA while not as accurate as RSA for the CFSS and IV, can also produce persistent oscillations of the global level number variance (GV) and better describes saturation level rigidity as a function of the running energy. Overall, it is the most reliable method for a wide range of statistics.

A key component of natural photosynthesis are the antenna chromophores (chlorophylls and carotenoids) that capture solar energy and direct it towards the reaction centers of photosystems I and II. Highlighted by highly-ordered crystal structures and synthetic tunability via crystal engineering, metal–organic frameworks (MOFs) have the potential to mimic the natural photosynthetic systems in terms of the efficiency and directionality of energy transfer. Owing to their larger surface areas, MOFs have large absorption cross sections, which amplifies the rate of photon collection. Furthermore, MOFs can be constructed using analogues of chlorophyll and carotenoids that can participate in long-range energy transfer. Herein, we aimed to design photoactive MOFs that can execute one of the critical steps involved in photosynthesis - photon collection and subsequent energy transfer. The influence of spatial arrangement of chromophores on the efficiency and directionality of excitation energy transfer (EET) was investigated in a series of mixed-ligand pyrene- and porphyrin-based MOFs. Due to the significant overlap between the emission spectrum of 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy) and the absorption spectrum of meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP), the co-assembly of these two ligands in a MOF should enable facile energy transfer. Bearing this in mind, three TBAPy-based MOFs with markedly different network topologies (ROD-7, NU-901, and NU-1000) were chosen and a small number of TCPP units were incorporated in their backbone. To gain insight into the photophysical properties of mixed-ligand MOFs, we conducted time-resolved and steady-state fluorescence measurements on them. Stern-Volmer analysis was performed on the fluorescence lifetime data of mixed-ligand MOFs to determine the quenching constants. The quenching constant values for ROD-7, NU-901, NU-1000, and TBAPy solution were found to be 15.03 ± 0.82 M-1, 10.25 ± 0.99 M-1, 8.16 ± 0.41 M-1, and 3.35 ± 0.30 respectively. In addition, the ratio of the fluorescence intensities of TCPP and TBAPy was used to calculate the EET efficiencies in each of the three MOFs. EET efficiencies were in the following order: ROD-7 > NU-901 > NU-1000 > TBAPy-solution. Based on the trends observed for quenching constants and EET efficiencies, two conclusions were drawn: (1) the ligand-to-ligand energy transfer mechanism in MOFs outperforms the diffusion-controlled mechanism in solution phase, (2) energy transfer in MOFs is influenced by their structural parameters and spectral overlap integrals. The enhanced EET efficiency in ROD-7 is attributed to shorter interchromophoric distance, larger orientation factor, and larger spectral overlap integral. Directionality of energy transfer in these MOFs was assessed by calculating excitonic couplings between neighboring TBAPy linkers using the atomic transition charges approach. Rate constants of EET (kEET) along different directions were determined from the excitonic couplings. Based on the kEET values, ROD-7 is expected to demonstrate highly anisotropic EET along the stacking direction. In order to explore the mechanistic aspects of EET in porphyrin-based MOFs, we studied the energy transfer characteristics of PCN-223, a zirconium-based MOF containing TCPP ligands. After performing structural characterization, the photophysical properties of PCN-223 and free TCPP were investigated using steady state and time-resolved spectroscopy. pH-dependent fluorescence quenching experiments were performed on both the MOF and ligand. Stern-Volmer analysis of quenching data revealed that the quenching rate constants for PCN-223 and TCPP were 8.06 ± 1011 M-1s-1 and 2.71 ± 1010 M-1s-1 respectively. The quenching rate constant for PCN-223 is, therefore, an order of magnitude larger than that for TCPP. Additionally, PCN-223 demonstrated a substantially higher extent of quenching (q = 93%) as compared to free TCPP solution (q = 51%), at similar concentrations of quencher. The higher extent of quenching in MOF is attributed to energy transfer from neutral TCPP linkers to N-protonated TCPP linkers. Using the Förster energy transfer model, the rate constant of EET in PCN-223 was calculated. The magnitude of rate constant was in good agreement with the kEET values reported for other porphyrin-based MOFs. Nanosecond transient absorption measurements on PCN-223 revealed the presence of a long-lived triplet state (extending beyond 200 μs) that exhibits the characteristic features of a TCPP-based triplet state. The lifetime of MOF is shorter than that of free ligand, which may be attributed to triplet-triplet energy transfer in the MOF. Lastly, femtosecond transient absorption spectroscopy was employed to study the ultrafast photophysical processes taking place in TCPP and PCN-223. Kinetic analysis of the femtosecond transient absorption data of TCPP and PCN-223 showed the presence of three distinct time components that correspond to: (a) solvent-induced vibrational reorganization of excitation energy, (b) vibrational cooling, and (c) fluorescence. Materials that allow control over the directionality of energy transfer are highly desirable. Core-shell nanocomposites have recently emerged as promising candidates for achieving long-distance, directional energy transfer. For our project, we aim to employ UiO-67-on-PCN‐222 composites as model systems to explore the possibility of achieving directional energy transfer in MOF-based core-shell structures. The core–shell composites were synthesized by following a previously published procedure. Appropriate amounts of Ruthenium(II) tris(5,5′-dicarboxy-2,2′-bipyridine), RuDCBPY, were doped in the shell layer to produce a series of Ru-UiO-67-on-PCN‐222 composites with varying RuDCBPY loadings (CS-1, CS-2, and CS-3). The RuDCBPY-doped core–shell composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) imaging, Nitrogen adsorption-desorption isotherms, and diffuse reflectance spectroscopy. Efforts are currently underway to quantify RuDCBPY loadings in CS-1, CS-2, and CS-3. After completing structural characterization, the photophysical properties of CS-1, CS-2, and CS-3 will be investigated with the help of time-resolved and steady-state fluorescence spectroscopy.
Doctor of Philosophy
The pigment−protein complexes in natural photosynthetic units (also known as light harvesting antennas) efficiently capture solar energy and transfer this energy to reaction centers that carry out water splitting reactions. The collective chromophoric behavior of antennas can be replicated by metal-organic frameworks (MOFs). MOFs are crystalline, self-assembled materials composed of metal clusters connected by organic molecules. In this dissertation, we study the factors that govern the energy transfer and light harvesting capabilities of MOFs. In chapter 2, we examined the role of 3D structure of MOFs in energy transfer. In chapter 3, we investigated the influence of pH and temperature on the photophysical properties of MOFs. In chapter 4, we explored the possibility of energy transfer in novel MOF-on-MOF composites. This work is intended to pave the way for the construction of highly efficient MOF-based materials that can serve as the light harvesting and energy-transfer components in solar energy conversion devices.

This book demonstrates how cheetahs are adapted to arid savannahs like the southern Kalahari, and makes comparisons with other areas, especially the Serengeti. Topics dealt with are: demography and genetic status; feeding ecology, i.e. methods used for studying diet, diets of different demographic groups, individual diet specializations of females, prey selection, the impact of cheetah predation on prey populations, activity regimes and distances travelled per day, hunting behaviour, foraging success and energetics; interspecific competition; spatial ecology; reproductive success and the mating system; and conservation. The major findings show that cheetahs are well adapted to arid ecosystems and are water independent. Cheetah density in the study area was stable at 0.7/100 km2 and the population was genetically diverse. Important prey were steenbok and springbok for females with cubs, gemsbok, and adult ostrich for coalition males, and steenbok, springhares, and hares for single animals. Cheetahs had a density-dependent regulatory effect on steenbok and springbok populations. Females with large cubs had the highest overall food intake. Cheetahs, especially males, were often active at night, and competition with other large carnivores, both by exploitation and interference, was slight. Although predation on small cubs was severe, cub survival to adolescence was six times higher than in the Serengeti. There was no difference in reproductive success between single and coalition males. The conservation priority for cheetahs should be to maintain protected areas over a spectrum of landscapes to allow ecological processes, of which the cheetah is an integral part, to proceed unhindered.

The rising number and capacity requirements of wireless systems bring increasing demand for RF spectrum. Cognitive radio (CR) system is an emerging concept to increase the spectrum efficiency. CR system aims to enable opportunistic usage of the RF bands that are not occupied by their primary licensed users in spectrum overlay approach. In this approach, the major challenge in realizing the full potential of CR systems is to identify the spectrum opportunities in the wide band regime reliably and optimally. In the spectrum underlay approach, CR systems enable dynamic spectrum access by co-existing and transmitting simultaneously with licensed primary users without creating harmful interference to them. In this case, the challenge is to transmit with low power so as not to exceed the tolerable interference level to the primary users. Spectrum sensing and estimation is an integral part of the CR system, which is used to identify the spectrum opportunities in spectrum overlay and to identify the interference power to primary users in spectrum underlay approach. In this chapter, the authors present a comprehensive study of signal detection techniques for spectrum sensing proposed for CR systems. Specifically, they outline the state of the art research results, challenges, and future perspectives of spectrum sensing in CR systems, and also present a comparison of different methods. With this chapter, readers can have a comprehensive insight of signal processing methods of spectrum sensing for cognitive radio networks and the ongoing research and development in this area.

This chapter describes the origins of medieval Jewish philosophy as a response to a threat. Philosophy was undoubtedly regarded as a threat by many medieval thinkers, Jewish as well as Muslim. In the Jewish milieu, the perceived threat was reinforced by a deep-seated antipathy towards all alien literature that is evidenced in classic rabbinic writings. There was, nonetheless, a minority of medieval Jewish thinkers who did not regard philosophy as a menace. This chapter thus weaves a composite figure out of a number of writers who dipped their toes in philosophy or plunged in head first. It focuses on the rationalist approach to the existence of God, the love of God, and the obligation to study the Torah. The writers from whom the composite image is drawn are not all cut from the same cloth and would not all agree with everything to be said here. There would be demurrals, especially regarding the proposition that philosophy formed an integral component of the rabbinic curriculum. The composite portrait nevertheless captures the overall attitude of the segment of the medieval Jewish spectrum that qualifies as rationalist.

This paper investigates the behaviour of a bottom hinged flap-type wave energy converter (WEC), namely the Oscillating Wave Surge Converter (OWSC), in random seas. The semi-analytical model of Renzi and Dias (2013b) for an OWSC in the open ocean is considered to analyze the performance of the device in random incident waves. The modelling is performed within the framework of a linear potential flow theory, by means of Green’s integral theorem. The resultant hypersingular integral equation for the velocity potential obtained from the above formulation is solved using a series expansion in terms of Chebyshev polynomials of the second kind. The behaviour of the device is investigated for six different sea states, generally representative of the wave climate in the North Atlantic Ocean at the European Marine Energy Centre test site. A Bretschneider spectrum is considered in order to reproduce the sea climate. The analysis is made for sea states where the spectral energy contribution from large periods, which cause excitation of body resonance of the flap — not modelled by the linear theory — is almost negligible. The power take-off damping is optimised for each individual sea state to calculate the captured power. The investigation is undertaken for two flaps of different widths, resembling the Oyster1 and the new Oyster800 version of the Oyster WEC, respectively. Comparison is made between the performances of the two converters. The effect of varying the width and the characteristic parameters of the flap on the capture factor in random seas is then discussed. The results of the analysis show that the performance of the device is fairly consistent for the sea states considered. Also an enhancement in the overall average capture factor is shown for the latest version of the wave energy conversion device.

The intent of this paper is the presentation and discussion of a methodology for the evaluation and analysis of seismic loads effects on a nuclear power plant. To help in focussing the presented methodology, a preliminary simplified analysis of an integral, medium size next generation PWR reactor structure (IRIS project, an integral configuration PWR under study by an international group) was considered as an application example also for models/codes evaluation. The performed preliminary seismic analysis, even though by no means complete, is intended to evaluate the method of calculating the effects of dynamic loads propagation to the reactor internals for structural design as well as geometrical and functional optimisation purposes. To this goal, finite element method and separated (sub) structures approaches were employed for studying the overall dynamic behaviour of the nuclear reactor vessel. The analysis was set up by means of numerical models, implemented on the MARC FEM code, on the basis of Design Response Spectra as indicated on the relevant rules for Nuclear Power Plants (NRC 1.60) design. The seismic analysis is indented to evaluate the dynamic loads propagated from the ground through the Containment System and Vessel to the Steam Generator’s tubes.

Unobstructed PIV measurements within complex turbomachinery flow fields are performed in an optical-refractive-index-matched facility consisting of a 2-stage axial turbomachine. Two different test setups are utilized to demonstrate wake-wake, wake-blade interactions and the associated flow non-uniformities and turbulence. The flow consists of a lattice of interacting wake segments, which are being chopped by the rotor and stator blades. The wake fragments become discontinuous due to the velocity differences across the rotor blades. Striking flow phenomena that occur as a result of this non-uniform flow field, such as turbulent “hot spots” and kinking of the rotor wake are presented at high magnification and samples that are large enough to obtain converged statistics. In this paper we focus on the flow field and turbulence within the rotor wake. One thousand instantaneous realizations at the same phase are used for determining the phase averaged flow and turbulence statistics including Reynolds stresses, turbulence spectra, production, dissipation, and mean strains. Three methodologies are adopted to investigate the details of the rotor wake structure: 1. Local maximization of 2-D shear strain and Reynolds shear stress; 2. 1-D energy spectral analysis; and 3. Subgrid-Scale (SGS) energy budget. Alignment of the local coordinates with direction that maximizes the local shear strain shows that except for the hot spot regions the rotor wake consists of two parallel layers exposed to planar shear strain. The normal strains in this system are significantly lower, indicating that out-of-plane normal straining is much weaker than the in-plane shear (except near the hot spot and close to the trailing edge of the rotor). Significant differences exist in several regions between the orientation of a coordinate system that maximizes the shear strain, and the system that maximizes the Reynolds shear stress, particularly around the hot spot, near the trailing edge, and within the stator wake segments on both sides of the rotor wake. 1-D spectral analysis reveals that the turbulence near the trailing edge is anisotropic and highly dissipative. The dissipation decreases and turbulence becomes more isotropic further away from the trailing edge, but becomes anisotropic again near the hot spot. Spatial filtering of data and measurement of the resulting SGS stresses enable us to examine and compare energy fluxes from the mean flow to the resolved and subgrid scales, as well as from the resolved to the subgrid scales. Due to the limitation in resolution, the present filter scale is 50% of the integral scale (∼wake width). Consequently, the energy flux from the mean flow to the subgrid scales is much higher than flux from the resolved turbulence to the subgrid scales. The production term, representing the energy flux from the mean flow to the resolved scales is typically higher than the flux from the resolved to the subgrid scales. Thus, build-up of large-scale energy occurs in substantial part of the near wake. The dissipation rates estimated from the spectra are everywhere (including the hot spot) of the same order as the overall SGS dissipation rate.

Abstract Three-dimensional numerical simulations of turbulent mixing at a perturbed interface of a dense shell compressed by a spherically imploding shock wave are presented. This case is a simplified version of inertial confinement fusion implosion (ICF) where a small capsule containing nuclear material is compressed to extremely high pressure and temperature to achieve fusion burn. The current simulations were performed using a high-order spherical method and a semi-Lagrangian moving mesh algorithm implemented in our in-house code Flamenco. Results of narrowband and broadband initial perturbations are presented at different grid resolutions along with mix layer limits, molecular mixing, turbulent kinetic energy and bubble/spike heights. The initial multimode perturbations applied at the interface consist of a superposition of cosine waves and are determined according to a specified power spectrum and standard deviation. These are employed in a spherical segment, enabling the efficient computation of a wide range of low to relatively high mode-number perturbations. The overall grid convergence of the solution is analysed and the different findings from the integral quantities and bubble/spike amplitudes are indicated.

In nuclear plant piping systems thermal fatigue damage can arise at locations where there is turbulent mixing of different temperature flows. The severity of this phenomenon is difficult to assess via plant instrumentation due to the high frequencies involved. NESC report EUR 22763 EN, published in 2007, defines the “Level 1” screening criterion for the design of austenitic stainless steel mixing tees, based on recorded incidents of fatigue cracking in civil power plants. The experimental data indicates that damage due to High Cycle Thermal Loading (HCTL) is unlikely to occur if the temperature difference between the hot and cold inlet streams is less than 80°C. The “Level 2” approach outlined by NESC provides a methodology for the calculation of a fatigue usage factor based on the assumption of a sinusoidal thermal loading at the most damaging frequency for a given ΔT. Advice is given on selection of heat transfer coefficient, fatigue curves, fatigue strength reduction factors and plasticity correction factors. Experience shows that these methods can be overly pessimistic when compared with plant operational experience. This paper describes a case study using the more detailed NESC “Level 3” evaluation of HCTL at a Pressurised Water Reactor (PWR) mixing tee using a coupled Computational Fluid Dynamics and Finite Element Analysis (CFD/FE) analysis to evaluate the complete load spectra together with the ASME 2010 fatigue S-N curve. The CFD model used is “conjugate”, ie it calculates temperatures in both the fluid and the metal. Large Eddy Simulation (LES) was used to investigate HCTL effects using an appropriate mesh size to accurately predict the rapid fluctuations in metal temperature local to the surface. Metal temperature predictions using conjugate CFD analyses provided the input to finite element analysis, utilising rain-flow techniques, in order to derive fatigue usage factors in the areas of interest. This study found that the severity of HCTL is influenced by various factors such as flow conditions, local geometry including bore match features, integral conical reducers that allow progressive change in pipe radius as well as branch pipe swirl penetration.

Wake control by boundary layer suction has been applied to a high-lift low-pressure turbine blade with the intention of reducing the wake velocity defect, hence attenuating wake-blade interaction, and consequently the generation of tonal noise. The experimental investigation has been performed in a large scale linear turbine cascade at midspan. Two Reynolds number conditions (Re = 300000 and Re = 100000), representative of the typical operating conditions of the low pressure aeroengine turbines, have been analyzed. Boundary layer suction has been implemented through a slot placed in the rear part of the profile suction side. The suction rate has been varied in order to investigate its influence on the wake reduction. Mean velocity and Reynolds stress components in the blade to blade plane have been measured by means of a two-component crossed miniature hot-wire. The wake shed from the central blade has been investigated in several traverses in the direction normal to the camber line at the cascade exit. The traverses are located at distances ranging between 5 and 80% of the blade chord from the blade trailing edge. To get an overall estimate of the wake velocity defect reductions obtained by the application of boundary layer suction, the integral parameters of the wake have been also estimated. Moreover, spectra of the velocity fluctuations have been evaluated to get information on the unsteady behaviour of the wake flow when boundary layer suction is applied. The results obtained in the wake controlled by boundary layer suction have been compared with the results in the baseline profile wake at both Reynolds number conditions for the purpose of evaluating the control technique effectiveness. The removal of boundary layer through the slot in the rear part of the profile suction side has been proved to be very effective in reducing the wake shed from the profile. The results show that a reduction greater than 65% of the wake displacement and momentum thicknesses at Re = 300000, and a reduction greater than 75% at Re = 100000 can be achieved by removal of 1.5% and 1.8% of the single passage through flow, respectively.