Добірка наукової літератури з теми "Decay stage"

A data base of arthropods of forensic importance was collected from pig carrions from 10th June to 10th August 2017 in the Warri city, 3 pigs were killed by cervical dislocation and left to decay while the daily assemblage of arthropods were collected from it. The result showed 5 stages of the carrion decomposition; fresh, bloated, active decay, advance decay and dry decay correspondingly despite that there was only a single sequence of decomposition. Entomofauna groups from 3 orders of Diptera, Coleoptera and Hymenoptera, with ten families were collected during the study while 233 insects were collected at the fresh stage, 324 were collected at the bloat stage, and 328 were recorded at the active decay stage, 405 at the advance decay stage and only 158 at the dry decay stage. The dominance index was high (0.09) at the dry decay stage but low (0.06) at the bloat, active decay and advanced decay stages. Shannon–Wiener index (H) was high (2.91) in the advanced decay stage but was low (2.52) at the dry decay stage. Arthropod from the orders of Diptera and Coleoptera were forensically significant as they used the carcasses for feeding and oviposition and could be used in the estimation of the post mortem interval while the order Hymenoptera used the carrion as extension of their habitat and as predatory ground to the necrophagous groups, it is advocated that more studies be carried out in different seasons using different animal models to create dependable data base of forensically importance arthropods in Warri and its environs.

Early stages of decay by two brown-rot fungi in two woods were studied by light and scanning electron microscopy. The earliest diagnostic feature to appear was hyphae in the earlywood lumina. The earliest effect on cell walls was the loss of birefringence in the earlywood; Poria placenta (syn. Postia placenta) caused this loss at the earliest stage of decay observed, in both Douglas-fir and white fir, while Gloeophyllum trabeum caused significant weight loss before loss of birefringence was visible. Attack on the latewood progressed from the earlywood, and was different in pattern among the wood/fungus combinations. Hyphal and bore hole diameter increased throughout the early progression of decay and would be useful in evaluating the stage of decay, if the starting diameter of hyphae could be determined. Separation between cells was not observed until moderate stages of decay and, therefore, was not useful in diagnosing early stages of decay.

Saproxylic insects, those associated directly or indirectly with decaying wood for all or part of their life cycle, compose a large proportion of forest organisms. Flies (Diptera) are often the most abundant and species-rich group of insects in forest microhabitats, yet most work to date on saproxylic insect diversity and ecology has focused on beetles (Coleoptera). We compared saproxylic Diptera assemblages reared from two tree species (sugar maple and American beech) at two stages of decay (early/young and advanced/old) for a total of 20 logs in an eastern Canadian Nearctic old-growth forest. We found that communities are distinct within both species type and decay stage of wood. Early decay stage wood is more variable in community composition than later decay stage; however, as the age of the decaying wood increases, the abundance of Diptera increases significantly. Most indicator species are discernible in later decay stage and wood type. We venture to suggest that stochastic and deterministic processes may play a role in driving Diptera communities in temperate deciduous forests. To retain the highest saproxylic Diptera diversity in a forest, a variety of decaying wood types at different stages of decomposition is necessary.

Hot-wire measurements are carried out in grid-generated turbulence at moderate to low Taylor microscale Reynolds number $Re_{{\it\lambda}}$ to assess the appropriateness of the commonly used power-law decay for the mean turbulent kinetic energy (e.g. $k\sim x^{n}$, with $n\leqslant -1$). It is found that in the region outside the initial and final periods of decay, which we designate a transition region, a power law with a constant exponent $n$ cannot describe adequately the decay of turbulence from its initial to final stages. One is forced to use a family of power laws of the form $x^{n_{i}}$, where $n_{i}$ is a different constant over a portion $i$ of the decay time during the decay period. Accordingly, it is currently not possible to determine whether any grid-generated turbulence reported in the literature decays according to Saffman or Batchelor because the reported data fall in the transition period where $n$ differs from its initial and final values. It is suggested that a power law of the form $k\sim x^{n_{init}+m(x)}$, where $m(x)$ is a continuous function of $x$, could be used to describe the decay from the initial period to the final stage. The present results, which corroborate the numerical simulations of decaying homogeneous isotropic turbulence of Orlandi & Antonia (J. Turbul., vol. 5, 2004, doi:10.1088/1468-5248/5/1/009) and Meldi & Sagaut (J. Turbul., vol. 14, 2013, pp. 24–53), show that the values of $n$ reported in the literature, and which fall in the transition region, have been mistakenly assigned to the initial stage of decay.

AUF1 promotes rapid decay of mRNAs containing 3′ untranslated region (3′UTR) AU-rich elements (AREs). AUF1 depletion in mice accelerates muscle loss and causes limb girdle muscular dystrophy. Here, we demonstrate that the selective, targeted degradation by AUF1 of key muscle stem cell fate-determining checkpoint mRNAs regulates each stage of muscle development and regeneration by reprogramming each myogenic stage. Skeletal muscle stem (satellite) cell explants show that Auf1 transcription is activated with satellite cell activation by stem cell regulatory factor CTCF. AUF1 then targets checkpoint ARE-mRNAs for degradation, progressively reprogramming the transcriptome through each stage of myogenesis. Transition steps in myogenesis, from stem cell proliferation to differentiation to muscle fiber development, are each controlled by fate-determining checkpoint mRNAs, which, surprisingly, were found to be controlled in their expression by AUF1-targeted mRNA decay. Checkpoint mRNAs targeted by AUF1 include Twist1, decay of which promotes myoblast development; CyclinD1, decay of which blocks myoblast proliferation and initiates differentiation; and RGS5, decay of which activates Sonic Hedgehog (SHH) pathway-mediated differentiation of mature myotubes. AUF1 therefore orchestrates muscle stem cell proliferation, self-renewal, myoblast differentiation, and ultimately formation of muscle fibers through targeted, staged mRNA decay.

We examined the effects of woody substrate and stand age on diversity and relative abundance of bryophytes, lichens, and fungi in trembling aspen (Populus tremuloides Michx.) mixedwood boreal forests in Alberta. Point sampling was carried out on surfaces of downed woody material in young (23-26 years), mature (51-63 years), and old (122-146 years) aspen mixedwood stands. Downed woody material was categorized into one of seven decay stages. Diversity and relative abundance of bryophytes, lichens, and fungi were related to decay stage of the log and to stand age. Old aspen mixedwood stands had the highest nonvascular species richness and the greatest diversity of woody substrates in each of the decay stages. The seven decay stages shared many species. Species of bryophytes, lichens, and fungi on particular decay stages were different across the age-classes, indicating that time, as well as structural attributes, were important in determining species assemblages. These results suggest that both the presence of old aspen mixedwood stands and downed wood in different stages of decay are important to maintaining assemblages of bryophytes, lichens, and fungi.Key words: bryophytes, lichens, decay, aspen mixedwood, downed woody material.

Mixed beech (Fagus orientalis Lipsky) forests are very important to the Hyrcanian region of Iran because of their high degree of naturalness and as a source of wood production. Determination of tree spatial patterns over development stages is a first step in understanding underlying processes driving regeneration and forest dynamics. Spatial patterns of trees from three development stages (initial, optimal and decay) of an untouched mixed beech forest were quantified within three 1-ha plots. To prepare the stem maps, we measured each tree with a DBH larger than 7.5 cm using the azimuth-distance method. Spatial patterns were then analysed using Ripley’s K-function. Results indicated that the number of trees decreased from the initial stage to the decay stage, with tree spatial patterns being aggregated, slightly aggregated and highly randomized for initial, optimal and decay stages, respectively. Differences in spatial patterns among the development stages are not unexpected considering that such unmanaged forests are driven by gap dynamics which results in interactions between gap filling individuals.

The domestic pig (Sus scrofa) was used as a model to study arthropod succession on carcasses under tree shade and out of shade in southern Nigeria. Carcass decomposition took longer periods under tree shade than in exposed sites, at 24.5 and 16.5 days, respectively. Four decomposition stages - fresh, bloated, decay, and dry - were observed. No significant variabilities were recorded in the types and patterns of infestation of the carcasses by arthropods in both locations. Four classes of arthropods - Insecta, Arachnida, Diplopoda and Crustacea - were recorded. The class Insecta dominated the total arthropods collected with 24 families, and formed 94% of the catches. The other three classes each had one family represented, and contributed only 2% of the total catches. The calliphorids, a phorid, and sarcophagids arrived and bred on the carcasses only a few hours after death of the pigs. Families of coleopterans came during the bloated stage, and fed on the immature dipterous maggots and carrion materials. The ants (Hymenoptera) came in large numbers to eat the carcasses, and also preyed on all other fauna of the food resource. A muscid and a stratiomyiid, bred on the carcass as to the decay stage. Other insects and arthropods arrived mostly during the decay stage to feed on the carcasses. Species richness on the carcasses peaked during the decay stage.

<p><em>Aim of study</em>: This study aimed to examine the dead wood inhabiting macrofungi communities occurring on dead beech and hornbeam trees in Caspian forests.<strong></strong></p><p><em>Area of study</em>: The Kheiroud forest in the north of Iran.</p><p><em>Material and Methods</em>: Data from 205 sampling dead tree were analyzed by means of Generalized Linear Models (GLM) to test the effects of decay stage, DBH, Length or Height on macrofungi diversity. Additionally, tree species, dead wood size, log position, decay stage were used as predictor factors for the number of sporocarps species (NSS) as a fungal species richness and diversity in each dead log using analysis of variance</p><p><em>Main results</em>: The number of sporocarps species (NSS) varied in different dead wood size and decay classes. The different stages of decay and the different size classes of dead wood had significantly different species richness of macrofungi. Deadwood in the high-decayed stages contained the highest diversity of fungi. Most of fungi identified on both logs and snags belonged to Basidiomycetes and Ascomycetes. The highest value for richness and evenness indices calculated in large diameter dead wood in decay class III. The results indicated the size and decay class of dead wood describe the greatest variance of the model that means the highest number of sporocarps species inhabited on the large dead wood in advanced stage of decaying.</p><p><em>Research highlights</em>: Macrofungi diversity varied significantly across pieces of dead wood with downed logs, larger pieces, and wood in later stages of decay having the highest macrofungi diversity.</p><p> <strong>Keywords</strong>: Caspian forest; coarse woody debris; down woody debris; Iran.<strong></strong></p>

Dental caries or tooth decay is one of the most prevalent bacterial infectious diseases of mankind. In recent oral health surveys, more than 60% of Australian teenagers surveyed had experienced the disease and most dentate adults surveyed exhibited multiple teeth affected by caries. Treating the consequences of dental caries accounts for over 50% of the total cost of providing dental services in Australia, which in 1998 was estimated at $2.6 billion. Dental caries is a dynamic process that is initiated by microbial biofilms on the tooth surfaces (dental plaque) resulting in a disturbance of the equilibrium between tooth mineral and the surrounding plaque fluid so that over time there is a net loss of mineral from the tooth surface. This demineralisation of the enamel may ultimately lead to cavitation of the surface of the tooth and once this stage of the disease has been reached only restorative methods (fillings) can be employed to limit the spread of decay and eventual loss of the tooth.

Loss of dead wood habitat and biodiversity has led to numerous excellent conservation based ecological and management studies. However, the structure of the xylophagous food web remains unclear for saproxylic xylophagous beetles and their parasitoid wasps, but fungi are believed to play an important role, both in direct and indirect nutritional acquisition and production of volatile chemicals. In the first study of its kind this thesis explores the importance of volatiles in host-searching behaviour and role of fungi in oviposition choice and larval nutrition, using three endophytic fungi, Stereum hirsutum, Stereum gausapatum and Eutypa spinosa, and two tree species Fagus sylvatica and Quercus robur, in early stage decay. Newly designed traps, excluding wood visual stimuli, provided the first evidence of wood-fungal volatile attraction by saproxylic wood-boring beetles, including primary and secondary xylophages, and their parasitoid wasps. Expanding on these results, the importance of fungi was further demonstrated through oviposition choice in field logs by two polyphagous cerambycid species. Ovipositing within or 20 mm from their preferred fungal species plug, females chose abiotic conditions suitable for sustaining fungal growth, suggesting a larval nutritional benefit. Further investigation, using one of the cerambycid species above, corroborated, via olfactometry, that volatiles from the preferred wood-fungal combination were attractants to gravid females, and induced ovipositor probing within the olfactometer. In addition, GC-EAG found six volatile compounds provoked an antennal response, including a monoterpene, two sesquiterpenes, an alkane and a ketone. Most importantly olfactometry and GC-EAG showed gravid females were unresponsive to wood or favored fungus presented singly. The result are discussed herein. In conjunction with the volatile only field trap experiment, a novel method to promote fungal only volatiles, by autoclaving the wood prior to sub-culturing, was trialed. GC-MS comparative analysis showed disparity between agar sub-cultured, autoclaved wood and natural wood with fungi, volatiles. This suggests that genes encoding cellulases and hemicellulases are regulated according to carbohydrate source, nutritional availability, oxygen and metal ions, supporting the variations observed. These results are discussed herein with regard to xylophagous beetles and their parasitoid wasps. The principal findings of this thesis are that wood-fungal interaction volatiles of the ephemeral early decay stage provide important olfactory host resource cues for saproxylic xylophagous beetles and their parasitoid wasps. Fungi, and particular, endophytic fungi, were shown to be a key component of the early stage xylophagous food web through volatile production, and as nutritional support evidenced by oviposition choice, olfactometry, GC-EAG and GC-MS analysis. This thesis has opened a new, exciting and important area of research with the potential to radically improve conservation management and employ a more holistic approach. These insights bring together the disparate research conducted individually on wood decay fungi, saproxylic xylophagous beetles and their parasitoid wasps

The introduction of general numerical methods in the form of widely available software can have a dramatic effect on the development of a scientific field. In electronic structure theory, for example, general-purpose programs (such as Gaussian, ADF, MOLPRO,. . . ) combined with better computational resources have in part led to molecular electronic structure calculations becoming a ubiquitous tool in chemical research. Similarly, quantum dynamics methods based on coupled time-evolving Gaussian basis sets and molecular potential energy surfaces calculated on-the-fly hold out similar promise in the study of non-adiabatic processes, because of their generality and freedom from ad hoc assumptions. Therefore, the aim of this thesis is to investigate the convergence and applicability of quantum dynamics calculations with a fully variational coupled Gaussian basis set description, termed variational Multi-Con guration Gaussian (vMCG). It is suggested that the vMCG approach provides a way to balance accuracy against computational cost for molecules of comparable size by choosing the number of coupled Gaussian product basis functions and a middle way forward between grid-based and trajectory surface hopping approaches to non-adiabatic molecular quantum dynamics calculations. In order to prove the suitability of vMCG we show its application to three problems of chemical interest: the study of fulvene excited state decay, the prediction of a coherent control mechanism for the same system and the benchmarking of an electronic population dynamics model for electronic transitions when occurring through a conical intersection. In the long term, the development of vMCG is expected to have a major impact, allowing nonadiabatic dynamics simulations to be made not only by theoreticians, but also by non-specialists and experimentalists in both industry and academia.Chapter 1: Modelling Excited State Decay [Diagrams appear here. To view, please open pdf attachment] This chapter introduces and reviews the current state-of-the-art modelling of non-adiabatic processes in molecular systems. This is a challenging topic since the simulation must treat simultaneously the motion of the nuclei and the electrons, which are coupled together. It is concluded that a wide range of methodologies are available. However, when looking for a general tool for the study of non-adiabatic processes, quantum dynamics methods based on coupled time-evolving Gaussian basis sets such as the Direct Dynamics variational Multi-Con guration Gaussian (DD-vMCG) wavepacket method, as well as to other related methods - such as Ab Initio Multiple Spawning (AIMS, FMS)[1, 2] and Multi-Con gurational Ehrenfest (MCE)[3, 4] - seem to be an especially suitable choice because of their generality and freedom from ad hoc assumptions. Chapter 2: variational Gaussian nuclear wavepackets [Diagrams appear here. To view, please open pdf attachment] This chapter describes three possible time-evolving Gaussian basis sets for use in non-adiabatic quantum dynamics based on the Direct Dynamics variational Multi-Con guration Gaussian (DD-vMCG) wavepacket method. These general model representations are compared using model calculations in a simple harmonic oscillator and describing their connections to other work. It is suggested that the fully variational nuclear wavefunction, termed vMCG (variational Multi-Con guration Gaussian) is a very convenient formulation leading towards a realistic sampling of the phase space without the initial conditions (i.e. initial disposition and momentum) being so important when using a su cient amount of coupled Gaussian basis functions. Chapter 3: Fulvene S1/S0 Excited State Decay [Diagrams appear here. To view, please open pdf attachment] The vMCG (variational Multi-Con guration Gaussian) approach described in Chapter 2 is benchmarked in a realistic system by modelling the radiationless decay from an electronic excited state through an extended conical intersection seam. As a benchmark system, we model the radiationless decay of fulvene from its rst electronic excited state and monitor two associated properties: the spatial extent to which the conical intersection seam is sampled and the timescale and stepwise nature of the population transfer. We illustrate how the use of a fully variational nuclear wavefunction provides a way to balance accuracy against computational cost for molecules of comparable size by choosing the number of coupled Gaussian product basis functions. Chapter 4: Controlling Fulvene S1/S0 Decay [Diagrams appear here. To view, please open pdf attachment] Direct quantum dynamics simulations using the vMCG (variational Multi- Con guration Gaussian) approach were performed in order to model the control of the stepwise population transfer in fulvene. As shown in Chapter 3, ultra-fast internal conversion takes place centred on the higher-energy planar/sloped region of the S1/S0 conical intersection seam. Therefore, two possible schemes for controlling whether stepwise population transfer occurs or not | either altering the initial geometry distribution or the initial momentum composition of the photo-excited wavepacket - were explored. In both cases, decay took place instead in the lower-energy twisted/peaked region of the crossing seam, switching o the stepwise population transfer. This absence of re-crossing is a direct consequence of the change in the position on the intersection at which decay occurs and its consequences should provide an experimentally observable fingerprint of this system. Chapter 5: A population transfer model for intramolecular electron transfer [Diagrams appear here. To view, please open pdf attachment] The aim of this chapter is to further prove the applicability of the vMCG (variational Multi-Con guration Gaussian) approach by benchmarking an approximate population dynamics model in Jahn-Teller systems. The socalled Density Matrix Non-Equilibrium Fermi Golden Rule (DM-NFGR) can be seen as a simpli ed version of vMCG, in which the nite Gaussian basis set and on-the-fly evaluation of the nuclear Hamiltonian are eliminated via use of the density matrix formalism and a perturbational treatment of the equations. This has three clear advantages: firstly, it allows us to extend the maximum molecular size considerably; secondly, we can relate the population dynamics to an analytical time-dependent rate expression; and finally, temperature effects can be included in the simulations. Benchmark calculations for the 2,6-bis(methylene) adamantyl (BMA) radical cation support the reliability of the results.

The question of a possible finite neutrino mass is one of the most investigated and controversial topics in particle physics and cosmology. The most promising direct ex periments for determining the neutrino mass are based on the study of the /-decay of molecular tritium. The mass of the neutrino is deduced by analysing the shape of the continuous energy spectrum of the electrons emitted in the /3-decay. In this thesis, the molecular physics issues facing these experiments are investigated. Theoretical final state probability distributions of the daughter molecule are calculated to satisfy the higher resolution requirements and increased sensitivity of the future ex periments. Transition probabilities to the six lowest electronically bound states of 3HeT+ are calculated. Rotational excitation of the daughter molecule is considered and probabilities obtained for the /-decay of T2 in the first four rotational states. Isotope contamination from DT and HT molecules is also investigated, and the probability distributions for 3HeD+ and 3HeH+ are calculated. The sensitivity of the initial temperature, ortho:para ratio and isotopic composition of the source is considered. Estimates of the error in the value of the neutrino mass deduced from fitting theoretical spectra, due to uncertainties in temperature, ortho:para ratio of T2 and percentage of DT molecules, are obtained. The R-matrix method is used to treat the electronic continuum of 3HeT+. Reso nances converging to the first eight excited target states are obtained, and the transition probabilities to these resonances and background continuum are calculated. Endpoint effects due to the decay of other possible species in the source - T_, T, T+, T2", Tg and T - are also investigated. It is hoped that this data will be used as part of the forthcoming KATRIN experi ment.

Aquesta tesi doctoral se centra en l’estudi teòric i numèric de sistemes fotònics amb retroacció i múltiples línies de retard, en el límit en el que els temps de retard són molt més grans que les escales de temps intrínseques del sistema. Es consideren dos sistemes òptics amb retroacció: i) dos oscilıladors optoelèctronics (OEOs) acoblats mútuament amb retard i ii) un làser de semiconductor amb retard que depèn de l’estat mitjançant el filtrat freqüencial des de dues cavitats amb diferents longituds i freqüències centrals. Tot i que els dos sistemes tenen en comú la presència de múltiples línies de retard, es tracta de dos sistemes ben diferents. En el primer, intevenen en tot moment dos temps de retard. En el segon, en canvi, la llum pren una única línia de retard a cada moment; en aquest sistema, el valor del retard és seleccionat intrínsicament per l’estat del sistema d’entre dos valors diferents mitjançant el filtrat freqüencial de la llum des de dos filtres de diferents freqüències centrals colılocats en dues cavitats de diferent longitud. D’una banda, es modelitzen aquests sistemes i es desenvolupen mètodes analítics per trobar solucions aproximades. Aquests mètodes es podrien emprar per entendre la dinàmica d’altres sistemes amb retard. D’altra banda, es comparen els resultats analítics o experimentals amb simulacions numèriques. La tesi està dividida en quatre parts. Les parts I, II i IV contenen diversos capítols, mentre que la part III està formada per un únic capítol. La part I, Introducció, objectius, eines i resultats anteriors , està dividida en tres capítols: En el Capítol 1, primer s’introdueixen alguns exemples de sistemes en els quals la presència de retards determina les propietats dinàmiques del sistema i en alguns casos origina un comportament complex. A continuació, s’introdueix el problema genèric d’un sistema amb retard i la seva modelització mitjançant equacions diferencials amb retard. S’expliquen dos exemples en detall, incloent la seva modelització amb equacions diferencials amb retard. Més endavant, s’introdueixen les ones quadrades que es poden obtenir amb sistemes d’OEOs i altres sistemes amb retard, i es presenten algunes aplicacions de les solucions tipus ona quadrada obtingudes amb OEOs, com són el control del període o la codificació d’informació. Finalment es resumeixen els objectius de la tesi. En el Capítol 2, es presenten alguns mètodes analítics i numèrics emprats en aquesta tesi, com són el mètode d’estabilitat lineal, l’estudi de l’estabilitat de solucions periòdiques, i algoritmes per integrar numèricament equacions diferencials amb retard. El Capítol 3 està dedicat a l’estudi de la dinàmica de sistemes senzills en els quals els sistemes d’estudi d’aquesta tesi estan basats: un oscilılador optoelectrònic i un làser de semiconductor amb retroacció òptica. En cada cas, es descriu el sistema en detall, s’introdueix la seva modelització mitjançant equacions diferencials amb retard, i es presenten els diferents tipus de dinàmica i possibles aplicacions. La part II està dedicada a la Sincronització en oscil·ladors optoelectrònics mú- tuament acoblats amb retard i conté quatre capítols: En el Capítol 4, es descriu el sistema de dos OEOs mútuament acoblats i amb dos temps de retard diferents, el de la retroacció i el de l’acoblament. Primer s’obtenen les equacions dinàmiques del sistema. A continuació, s’escriuen les equacions dinàmiques de manera adimensional i es troba l’estat estacionari estàtic (punt fix) del sistema. Per acabar, s’introdueix el cas d’OEOs idèntics, se simplifiquen les equacions dinàmiques i es demostra l’existència de solucions periòdiques sincronitzades en fase i en antifase a partir de l’anàlisi d’estabilitat lineal de la solució zero. El Capítol 5 se centra en la generació de solucions periòdiques quadrades mitjançant el sistema de dos OEOs idèntics mútuament acoblats descrit en el capítol 4, en el cas de retroacció negativa, la qual tendeix a reduir l’efecte de les pertorbacions de l’estat estacionari estàtic. Primer s’aplica el mètode d’estabilitat lineal per trobar el període de les solucions oscilılants en funció de la relació entre els dos temps de retard diferents. Es demostra la coexistència de múltiples solucions periòdiques de tipus ona quadrada sincronitzades en fase quan la raó entre el temps de retard intrínsec i el de l’acoblament satisfà una relació racional entre dos nombres senars. De manera similar, múltiples ones quadrades en antifase i amb diferents períodes poden coexistir quan la raó entre el temps de retard intrínsec i el de l’acoblament és un racional senar/parell. A continuació, s’apliquen mètodes assimptòtics per obtenir mapes per a l’amplada de les solucions. Es demostra que les solucions periòdiques quadrades experimenten una ruta al caos del tipus doblament de període. Després s’analitza l’efecte de canviar lleugerament els paràmetres en la forma de les solucions. Finalment, a partir del càlcul precís del període de les solucions, s’observa un fenomen de divisió del període en diferents valors. El Capítol 6 està dedicat a l’aparició de solucions quadrades estables amb el mateix model que en el Capítol 5, però en el cas de retroacció positiva, la qual tendeix a augmentar l’efecte de les pertorbacions de l’estat estacionari estàtic. Les solucions quadrades que apareixen amb retroacció positiva tenen un cicle asimètric i són més flexibles i robustes que les que s’obtenen amb retroacció negativa; en concret, l’asimetria del seu cicle permet que puguin adaptar la seva forma com a resposta a canvis en els valors dels paràmetres. Primer s’aplica l’anàlisi d’estabilitat lineal de l’estat estacionari estàtic per obtenir el període de les ones quadrades de freqüència més gran en funció de la relació entre els dos temps de retard diferents. Es demostra que el sistema té solucions sincronitzades en fase i en antifase, i que múltiples solucions poden coexistir, de manera similar al cas de retroacció negativa. No obstant això, a diferència del cas de retroacció negativa, aquí les solucions en antifase sempre coexisteixen amb solucions en fase amb diferents períodes. A més, aquest sistema té solucions periòdiques de freqüència més baixa, sincronitzades en fase i que coexisteixen amb les ones quadrades de freqüència alta per als mateixos valors dels paràmetres. A continuació, s’aplica un mètode assimptòtic per caracteritzar l’amplitud i la forma de les ones quadrades. Es demostra que el cicle de les solucions quadrades generades amb retroacció positiva es pot controlar canviant el voltatge constant aplicat als OEOs, sense que canviï el període. També s’analitza l’efecte de canviar lleugerament els valors dels paràmetres en la forma de les solucions. Es demostra que les ones quadrades generades amb retroacció positiva són més robustes a canvis en els valors dels paràmetres. Finalment, a partir del càlcul precís del període de les solucions, s’observa un fenomen de divisió del període en diferents valors. En el Capítol 7, s’estudia el cas de dos oscilıladors no-idèntics, incloent les possibilitats de retroacció negativa, positiva i mixta. Es demostra que aquest sistema pot generar múltiples solucions de tipus ona quadrada, amb diferents tipus de sincronització (en fase, en antifase i a un quart del període) depenent del signe de la retroacció de cada oscilılador. Les ones quadrades amb sincronització a un quart del període apareixen principalment quan la retroacció és negativa per a un oscilılador i positiva per a l’altre. Finalment, s’analitza la robustesa de les solucions sincronitzades a un quart del període a petits canvis en els valors dels paràmetres. La part III se centra en el tema Sistemes fotònics amb retards que depenen de l'estat i està formada per un capítol: En el Capítol 8, es considera un sistema de làser de semiconductor amb filtrat freqüencial des de dues cavitats de longituds i freqüències centrals diferents, com a model per a estudiar la dinàmica d’un sistema amb retard que depèn de l’estat. Primer s’introdueix el disseny experimental, que està basat en un làser de semiconductor i dos filtres de Bragg amb diferents freqüències centrals colılocats en dues cavitats de diferents longituds, i per tant associats a dos temps de retard diferents. Es demostra que la dinàmica d’aquest sistema es caracteritza per salts erràtics entre els dos valors del temps de retard. A continuació, s’introdueix un model teòric amb filtrat lorentzià des de dues cavitats diferents. Es calculen les solucions estacionàries i s’analitza la dinàmica erràtica amb retard que depèn de l’estat per a diferents valors dels paràmetres. Es demostra que els resultats numèrics en el règim erràtic coincideixen qualitativament amb els experiments. També es demostra que aquest sistema té solucions més regulars, similars a les ones quadrades periòdiques, amb retard que depèn de l’estat. Finalment, s’analitza l’estadística dels temps de residència durant els quals el retard pren un valor constant. La part IV, Resum i perspectives de treball, conté dos capítols de conclusions: el Capítol 9, corresponent a la part dels OEOs; i el Capítol 10, referit a la part dels retards depenents de l’estat. En aquests capítols es resumeixen els principals resultats obtinguts i es proposen algunes perspectives per a futures investigacions.
Esta tesis doctoral se centra en el estudio teórico y numérico de sistemas fotónicos con realimentación y múltiples líneas de retardo, en el límite en el que los tiempos de retardo son mucho más grandes que las escalas de tiempo intrínsecas del sistema. Se consideran dos sistemas ópticos con realimentación: i) dos osciladores optoelectrónicos (OEOs) mutuamente acoplados con retardo y ii) un láser de semiconductor con retardo dependiente del estado mediante el filtrado frecuencial desde dos cavidades con diferentes longitudes y frecuencias centrales. Aunque estos dos sistemas tienen en común la presencia de múltiples líneas de retardo, se trata de dos sistemas bastante diferentes. En el primero en todo momento intervienen dos tiempos de retardo. En el segundo, en cambio, la luz toma una única línea de retardo en cada momento; en este sistema, el valor del retardo es seleccionado intrínsicamente por el estado del sistema entre dos valores diferentes mediante el filtrado frecuencial de la luz desde dos filtros con diferentes frecuencias centrales colocados en dos cavidades de diferente longitud. Por un lado, se modelizan estos sistemas y se desarrollan métodos analíticos para encontrar soluciones aproximadas. Estos métodos podrían utilizarse para comprender la dinámica de otros sistemas con retardo. Por otro lado, se contrastan los resultados analíticos o experimentales con simulaciones numéricas. La tesis está dividida en cuatro partes. Las partes I, II y IV contienen varios capítulos, mientras que la parte III está formada por un solo capítulo. La parte I, Introducción, objectivos, herramientas y resultados anteriores , está dividida en tres capítulos: En el Capítulo 1, primero se introducen algunos ejemplos de sistemas en los cuales la presencia de retardos determina las propiedades dinámicas del sistema, en algunos casos dando lugar a comportamiento complejo. A continuación se presenta el problema general de un sistema con retardo y su modelización con ecuaciones diferenciales con retardo. Se explican dos ejemplos en detalle, incluyendo su modelización con ecuaciones diferenciales con retardo. Luego se introduce el régimen dinámico de oscilación periódica de tipo onda cuadrada que se puede obtener con OEOs y otros sistemas con retardo, y se resaltan algunas aplicaciones de estas ondas cuadradas, como el control del período y la codificación de información. El capítulo termina con un resumen de los objetivos de la tesis. En el Capítulo 2, se introducen algunos métodos numéricos y teóricos usados en esta tesis, como el análisis de estabilidad lineal, métodos y herramientas para el estudio de la estabilidad de soluciones periódicas, y algoritmos para integrar numéricamente las ecuaciones diferenciales con retardo. El Capítulo 3 está dedicado al estudio de la dinámica de sistemas sencillos en los que se basan los sistemas estudiados en esta tesis: un único OEO y un láser de semiconductor con realimentación óptica. En cada caso, se describe en detalle el sistema, se introduce su modelización con ecuaciones diferenciales con retardo, y se presentan sus diferentes regímenes dinámicos y posibles aplicaciones. La parte II está dedicada a la Sincronización en osciladores optoelectrónicos mutuamente acoplados con retardo y contiene cuatro capítulos: En el Capítulo 4, se describe el sistema de dos OEOs mutuamente acoplados y con dos tiempos de retardo diferentes, el de la propia realimentación y el del acoplamiento. Primero se derivan las ecuaciones dinámicas del sistema. A continuación se escriben las ecuaciones dinámicas en forma adimensional y se calcula la solución estacionaria estática (punto fijo) del sistema. Finalmente se introduce el caso de OEOs idénticos, se simplifican las ecuaciones dinámicas y se demuestra que el análisis de estabilidad lineal de la solución cero da lugar a soluciones periódicas sincronizadas en fase y en antifase. El Capítulo 5 se centra en la generación de pulsos simétricos de onda cuadrada mediante el sistema de dos OEOs idénticos mutuamente acoplados con retardo descrito en el capítulo 4, en el caso de realimentacion negativa, la cual tiende a reducir el efecto de las perturbaciones del estado etacionario estático. Primero se aplica el método de estabilidad lineal para obtener el período de las soluciones oscilatorias en función de la relación entre los dos tiempos de retardo diferentes. Se demuestra que múltiples soluciones periódicas de tipo onda cuadrada en fase coexisten cuando la razón entre el tiempo de retardo intrínseco y el del acoplamiento satisface una relación racional entre dos números impares. De manera similar, múltiples ondas cuadradas en antifase con diferentes períodos pueden coexistir cuando la razón entre el tiempo de retardo intrínseco y el del acoplamiento es un racional impar/- par. A continuación, se aplican métodos asintóticos para obtener mapas para la amplitud de las soluciones. Se demuestra que las ondas cuadradas periódicas experimentan una ruta al caos del tipo doblamiento de período. Después se analiza el efecto de cambiar ligeramente los valores de los parámetros en la forma de las soluciones. Finalmente, a partir del cálculo preciso del período de las soluciones, se observa un fenómeno de división del período en diferentes valores. El Capítulo 6 está dedicado a la aparición de pulsos de onda cuadrada estables con el mismo modelo que en el Capítulo 5 pero en el caso de realimentación positiva, la cual tiende a aumentar el efecto de las perturbaciones del estado etacionario estático. Las ondas cuadradas que surgen con realimentación positiva tienen un ciclo asimétrico y son más flexibles y robustas que las obtenidas con realimentación negativa; en particular, la asimetría de su ciclo les permite adaptar su forma en respuesta a cambios en los valores de los parámetros en vez de experimentar un doblamiento de período. Primero se aplica el análisis de estabilidad lineal del estado estacionario estático para obtener el período de las ondas cuadradas de mayor frecuencia en función de la relación entre los dos tiempos de retardo diferentes. Se demuestra que el sistema tiene soluciones sincronizadas en fase y en antifase, y que múltiples soluciones pueden coexistir, de manera similar al caso de realimentación negativa. Sin embargo, a diferencia del caso de realimentación negativa, aquí las soluciones en antifase siempre coexisten con soluciones en fase con diferentes períodos. Además, este sistema tiene soluciones periódicas de menor frecuencia, sincronizadas en fase y coexistiendo con las soluciones cuadradas rápidas para los mismos valores de los parámetros. A continuación se aplica un método asintótico para determinar la amplitud y forma de las ondas cuadradas. Se demuestra que el ciclo de las ondas cuadradas generadas con realimentación positiva se puede controlar cambiando el voltaje constante aplicado a los OEOs, manteniendo el período constante. También se analiza el efecto de variar ligeramente los valores de los parámetros en la forma de las soluciones. Se demuestra que las ondas cuadradas generadas con realimentación positiva son más robustas frente a cambios en los valores de los parámetros que las obtenidas con realimentación negativa. Finalmente, a partir del cálculo preciso del período de las soluciones, se demuestra que el período de las soluciones se divide en diferentes valores. En el Capítulo 7, se considera el caso de OEOs no idénticos, incluyendo las posibilidades de realimentación negativa, positiva y mixta. Se demuestra que este sistema puede generar múltiples ondas cuadradas, con diferentes tipos de sincronización (en fase, en antifase y a un cuarto del período) dependiendo del signo de la realimentación de cada oscilador. Las ondas cuadradas con sincronización a un cuarto del período aparecen principalmente cuando la realimentación es negativa para un oscilador y positiva para el otro. Finalmente se analiza la robustez de las soluciones sincronizadas a un cuarto del período frente a pequeños cambios en los valores de los parámetros. La parte III se centra en el tema Sistemas fotónicos con retardos que dependen del estado y está formada per un único capítulo: En el Capítulo 8, se considera un sistema de láser de semiconductor con filtrado frecuencial desde dos cavidades de longitudes y frecuencias centrales diferentes, como prototípico para estudiar la dinámica de un sistema con retardo que depende del estado. Primero se introduce el diseño experimental, basado en un láser de semiconductor con realimentación filtrada desde dos filtros de Bragg con diferentes frecuencias centrales y situados en dos cavidades de diferetes longitudes, y por lo tanto asociados a diferentes tiempos de retardo. Se demuestra que la dinámica de este sistema se caracteriza por saltos erráticos entre los dos valores del tiempo de retardo. A continuación se introduce un modelo teórico con filtrado lorenciano desde dos cavidades diferentes. Se calculan las soluciones estacionarias y se analiza la dinámica errática con retardo que depende del estado para diferentes valores de los parámetros. Se demuestra que los resultados numéricos en el régimen errático concuerdan de forma cualitativa con los resultados experimentales. También se demuestra que este sistema tiene soluciones más regulares, similares a las ondas cuadradas, con retardo dependiente del estado. Finalmente se analiza la estadística de los tiempos de residencia durante los que el retardo toma un valor constante. La parte IV, Resumen y perspectivas de trabajo , contiene dos capítulos de conclusiones: el Capítulo 9, correspondiente a la parte de los OEOs; y el Capítulo 10, referido a la parte de sistemas fotónicos con retardos dependientes del estado. En estos capítulos, se resumen los principales resultados obtenidos y se proponen algunas perspectivas de trabajo para futuras investigaciones.
This PhD thesis focuses on the theoretical and numerical study of photonic systems with feedback from multiple delay lines, in the limit in which the delay times are much longer than the intrinsic time scales of the system. Two optical systems with feedback are considered: i) two mutually delay-coupled optoelectronic oscillators (OEOs) and ii) a semiconductor laser with a delay time that depends on the state of the system via the filtered feedback from two cavities with different length and central frequency. Although these two systems have in common the presence of multiple delay lines, they are indeed quite different. In the former, two different delay times take part at any time. In the latter, in contrast, light takes a single delay line at any time; in this system, the delay time value is intrinsically selected among two different values by the state of the system since the frequency of light is selectively filtered by using two filters of different central frequencies placed in two cavities of different lengths. On the one hand, these systems are modelled and analytical methods are developed to find approximate solutions. These methods could be used to understand the dynamics of other systems with delay. On the other hand, extensive numerical simulations are compared to analytical or experimental results. The thesis is divided into four parts. Parts I, II and IV contain several chapters, whereas part III has a single chapter. Part I, Introduction, objectives, tools and previous results , is divided in three chapters: In Chapter 1, some examples of systems in which the presence of delays determines the dynamical properties of the system, often giving rise to complex behavior, are first introduced. After that, the generic problem of a system with delay and its modelling with delay differential equations is presented. Two examples are explained in detail, including their modelling with delay differential equations. Then, the square-wave periodic regime that can be obtained with OEOs and other systems with delay is introduced, and some applications of the square-wave regime are highlighted, such as the control of the period and information encoding. The chapter ends with a summary of the objectives of the thesis. Chapter 2 introduces some analytical and numerical methods and tools used in this thesis, such as the linear stability analysis, methods and tools for the study of the stability of periodic solutions, and algorithms to integrate numerically delay differential equations. Chapter 3 is devoted to the study of the dynamics of simple systems in which the systems studied in this thesis are based: a single OEO and a semiconductor laser with optical feedback. In each case, the system is described in detail, its modelling with delay-defferential equations is introduced, and its different dynamical regimes and possible applications are presented. Part II is devoted to the Synchronization in mutually delay-coupled optoelec- tronic oscillators and contains four chapters: Chapter 4 describes the system of two mutually delay-coupled OEOs with two different delay times, the self-feedback delay time and the coupling delay time. First, the dynamical equations of the system are derived. After that, the equations are writen in non-dimensional form and the steady state (fixed point) of the system is found. Finally, the case of identical OEOs is introduced, the dynamical equations are simplified and it is shown that the linear stability analysis of the zero solution gives rise to periodic solutions synchronized in phase and out of phase. Chapter 5 focuses on the generation of symmetric square-wave pulses by the system of two identical mutually delay-coupled OEOs described in Chapter 4, in the case of negative feedback, which tends to reduce the effect of the perturbations of the steady state solution. First, linear stability analysis is applied to obtain the period of the solutions as a function of the ratio between the two different delay times. It is shown that multiple in-phase square waves with different periods can coexist when the ratio between the self-feedback and the cross-feedback delay times satisfies a rational relationship involving two odd numbers. Similarly, multiple outof- phase square waves with different periodicity can coexist when the ratio between the self- and the cross-delay times is an odd/even rational. After that, asymptotic methods are applied to obtain maps for the amplitude of the solutions. It is found that the symmetric square-wave periodic solutions undergo a period doubling route to chaos. Then, the effect of the parameter mismatch in the form of the solutions is analyzed. Finally, a splitting of the period in different values is demonstrated by performing a precise calculation of the period of the solutions. Chapter 6 is devoted to the emergence of stable square-wave pulses with the system described in Chapter 4 in the case of positive feedback, which tends to amplify the effect of the perturbations of the steady state solution. The square waves arising with positive feedback have an asymmetric duty cycle and turn out to be more flexible and robust than those obtained with negative feedback; in particular, the asymmetry of their duty cycle allows them to adapt their shape in response to changes in the parameter values instead of undergoing a period doubling. First, the linear stability analysis of the steady state is applied to obtain the period of the oscillatory solutions as a function of the two different delay times. It is shown that the system has stable in- and out-of-phase synchronized solutions, and that several solutions can coexist, similarly to the case of negative feedback. Nevertheless, in contrast to the negative feedback case, here out-of-phase solutions always coexist with in-phase solutions with different periods. Furthermore, this system has limit cycles of lower frequency, synchronized in phase and coexisting with the aforementioned fast square waves for the same values of the parameters. After that, an asymptotic method is applied to determine the amplitude and the shape of the square waves. It is shown that the duty cycle of the square waves generated with positive feedback can be tuned with the constant voltage applied to the OEOs, while the total period remains constant. The effect of the parameter mismatch on the form of the solutions is also analyzed. It is found that the square waves generated with positive feedback are more robust to parameter mismatch than those obtained with negative feedback. Finally, a splitting of the period in different values is demonstrated by performing a precise calculation of the period of the solutions. Chapter 7 addresses the case of two non-identical OEOs, including the possibilities of negative, positive, and mixed feedback. It is shown that this system can generate multiple square-wave solutions, with different kinds of synchronization (in-phase, out-of-phase, or at a quarter of the period) depending on the sign of the feedback on each oscillator. The square waves with synchronization at a quarter of the period mainly appear when the feedback is negative for one oscillator and positive for the other one. Finally, the robustness of the solutions synchronized at a quarter of the period to parameter mismatch is analyzed. Part III focuses on the topic Photonic systems with state-dependent delays and contains a single chapter: In Chapter 8, a semiconductor laser system with frequency filtering from two cavities of different lengths and central frequencies is considered as prototypical to study the dynamics of a system with state-dependent delay. First, the experimental setup is presented. It is based on a semiconductor laser with filtered feedback from two Bragg filters of different central frequencies placed in two cavities of different lengths, and thus associated to different delay times, experiencing erratic jumps between the two delay-time values. Then, a theoretical model with lorentzian filtering from different cavities is introduced. The stationary solutions are calculated and the erratic dynamics with state-dependent delay is analyzed for different parameter values. It is shown that numerical results in the erratic regime are in qualitative agreement with the experiments. It is also shown that this system has more regular solutions, similar to the square waves, with state-dependent delay. Finally, the switching statistics is analyzed from the residence times during which the delay time remains constant. Part IV, Summary and future work , contains two concluding chapters: Chapter 9, corresponding to the part of OEOs; and Chapter 10, associated to the part of photonic systems with state-dependent delays. In these chapters, the main results are summarized and some perspectives of future work are proposed.

The evolution of views on the possibility of external influence on the process of radioactive decay is briefly presented. Such an effect can lead to the appearance of periods in the time series of the radioactive decay rate fluctuations, which have been the subject of intensive study in the last decade. Two mechanisms for identifying periods are considered: the study of deviations from the theoretical curve of the radioactive decay law and the study of the properties of fluctuations. It is shown that the latter method leads to a universal spectrum of periods observed not only in the time series of the radioactive decay rate fluctuations, but also in the time series of fluctuations of processes of various nature. The main object of our study are periods in the radioactive decay rate fluctuations. The presence of such periods suggests the possibility of external influence on the process of radioactive decay. Therefore, we briefly consider the evolution of views on the possibility of such an effect. To do this, we distinguish several stages. The division into stages is only partially historical, but, mainly, each stage characterizes a certain ideas that is implemented in it.

Abstract The post-fracture-pressure-decay (PFPD) technique is a low-cost method allowing for stage-by-stage hydraulic fracture characterization. The physics of the PFPD method are complex, with data affected by both hydraulic fracture and reservoir properties. Available analysis methods in the literature are oversimplified; reservoir or fracture properties are often assumed to be constant along the horizontal well, and therefore changes in the trend of pressure decay data are attributed to hydraulic fracture or to reservoir properties only. Moreover, methods analogous to those applied to the analysis of conventional diagnostic fracture injection tests (DFITs) are often used and ignore critical mechanisms involved in main-stage hydraulic fracture stimulation. A conceptual numerical simulation study was first conducted herein to understand the key physics involved in main-stage hydraulic fracturing. An analytical model was then developed to account for the dynamic behavior of the hydraulic fracture, pressure-dependent leakoff, proppant distribution, multiple fractures, and propped- and unpropped-closure events. The analytical model is cast in the form of a new straight-line analysis (SLA) method that provides stage-by-stage estimates of the ratio of unpropped fracture surface area to total fracture surface area. The SLA method was validated against numerical simulation results. Moreover, to account for the variation of reservoir properties along the horizontal well, the PFPD model is integrated with DFIT-flowback (DFIT-FBA) tests, performed at some points along the lateral, to obtain a reliable stage-by-stage hydraulic fracture and reservoir characterization approach. The practical application of the proposed integrated approach was demonstrated using PFPD and DFIT-FBA data from a horizontal well completed in 22 stages in the Montney Formation. The numerical simulation study demonstrated that the use of proppant and injection into multiple clusters (creating multiple fractures) results in multiple-closure events. The closure process may start early after the pump-in period at a pressure significantly higher than the minimum in-situ stress. Employing DFIT-based analytical models, which ignore the presence of proppant, causes significant errors in hydraulic fracture and reservoir property estimation. The PFPD field data examined herein exhibited a similar pressure trend to the numerical simulation cases. The ratio of unpropped fracture surface area to total fracture surface area was determined stage-by-stage using the PFPD SLA method, constrained by DFIT-FBA data. Engineers can use this information to optimize hydraulic fracture stimulation design in real-time, optimize well spacing, and forecast production. The cost and time advantages of this diagnostic method make this approach very attractive.

Abstract Unsteady blade row interaction (UBRI) has a large impact on performance in high speed axial compressors, thus, the influence of UBRI should be accurately predicted in compressor routine design. In this study, the unsteady rotor-stator interaction in a transonic single stage compressor, NASA Stage 35, is studied by steady and unsteady Reynolds-Averaged Navier-Stokes (RANS) methods. Firstly, the UBRI is analyzed. Periodic separation bubbles on stator suction surface induced by the rotor wake are observed. Comparisons between steady and unsteady results show that the radial distribution of flow angle near the hub and tip region of the stator is strongly influenced by UBRI. Secondly, deterministic correlations are analyzed based on the average-passage equation system (APES). The distribution of deterministic stress, the relationship between harmonics and decay rate of deterministic correlations, and the relationship between spatial correlations and deterministic correlations are analyzed. Results show that a strong non-linear interaction caused by the rotor wake and the stator potential field is found in the rotor-stator gap, and it is responsible for the generation of spatial-time correlation. It is found that the decay rate of deterministic correlation is highly related to the corresponding harmonics. The higher order harmonic owns higher decay rate. Then a modified exponential decay model for deterministic correlation based on harmonics is proposed, and shows a better performance. At last, the anisotropy of deterministic correlations is analyzed using Lumley triangle. Results show that the deterministic stress is highly anisotropic in the stator passage, which could be considered in the modeling if using similar strategy of turbulence modeling.

This paper addresses the significant differences in compressor rotor wake mixing loss which exist in a stage environment relative to a rotor in isolation. The wake decay for a rotor in isolation is due solely to viscous dissipation which is an irreversible process and thus leads to a loss in both total pressure and efficiency. Rotor wake decay in the stage environment is due to both viscous mixing and the inviscid strain imposed on the wake fluid particles by the stator velocity field. This straining process, referred to by Smith (1993) as recovery, is reversible and for a 2D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. It will be shown that for the rotor/stator spacing typical of core compressors, wake stretching is the dominant wake decay process within the stator with viscous mixing playing a secondary role. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated in isolation and in a stage configuration at near peak efficiency and near stall operating conditions. Additional insight is provided by a time-accurate 3D Navier Stokes simulation of the compressor stator flow field at the corresponding stage loading levels. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model, laser anemometer measurements, and simulations indicate that wake straining (stretching) is the primary decay process in the stator passage. The implications of these results on compressor stage design are discussed.

The occurrence of wood decay in common alder stems (Alnus glutinosa (L.) Gaertn.) was studied based on data obtained in seven matured stands in Latvia age ranging from 65 to 122 years. The study was intended as a pilot study to test the possible use of nondestructive micro-drill (Rinntech Resistograph® R650) for detection of the different stages of wood decay within common alder stems. The drilling profiles were visually compared with the wood samples obtained from increment borer or cross-cut sections at actual drilling height. The study confirmed initially proposed hypothesis that drilling profiles obtained using the Resistograph enabled the diagnosis of the common alder stem health condition. Wood decay stages – spongy rot and cavity can be detected successfully by the Resistograph; however, this non-destructive method does not detect discoloration in the wood, which is the earlier stage of wood decay. We found significant (p<0.05) positive correlation between decay occurrence and some of examined forest stand characteristics such as mean stand diameter, stand age and mean tree volume. The tree inspection showed that the preservation of old common alder stands can lead to a significant loss of wood quality. Based on this pilot study, we conclude that if the economic interests are prioritized in management of studied stands, the reduction of actual harvesting age of the common alder stands have to be considered.

Modern aircraft engine designs are driven towards higher operating temperature and lower coolant flow requirements. During the flight mission, the hot gas path components encounter flows at different pressure, temperature and turbulence conditions. During design of such components, there is always an interest towards fundamental understanding of the impact of inlet turbulence on overall performance. The paper presents aerodynamic performance (stage efficiency) impact of stator inlet viscosity ratio, decay rate and length scales in a cooled turbine rig, based on CFD studies only. Through CFD studies, it is observed that an inlet length scale variation by 10 times could impact the aerodynamic efficiency by ∼0.5% to 4% depending on the size of the length scale. Efficiency drops with higher flow length scales and turbulence intensity. The length scale effects are observed to be more predominant with high turbulence intensities than at low turbulence intensities. Similarly a viscosity ratio increase by 1000 times can decrease efficiency by < 0.5% in the lower bounds and can drastically increase to ∼ 3% at higher bounds. The efficiency drop can be as much as 2.5 % for a decay rate change from 0.01 to 1 for viscosity ratio of 10000.

This paper describes a computer code which solves viscous axisymmetric flow through multistage compressors. The code incorporates the modelling of 3-D effects which result from secondary flow and mixing and lead to property changes in the streamwise and spanwise directions. The method requires no extra data for loss, deviation and blockage. The necessary input data are the geometry, upstream stagnation conditions, rotational speed and mass flow rate. Blade wakes and their decay are modelled. The secondary flow component of the mixing coefficient modifies the uniform part and the result is used in the turbulent diffusion terms of the equation of motion. The P&W 3S1 low aspect ratio 3 stage compressor and UTRC 2 stage research compressor are used for validation. Considering the complexity of the flow in the multi-stage environment, it was concluded that the method gives encouraging results at a very economical rate.

Detailed measurements have been performed in a low pressure axial flow compressor stage to investigate the structure of the secondary flow field and the three-dimensional wake decay at different axial locations before and behind the rotor. The three dimensional flow field upstream and downstream of the rotor and on the centerline of the stator blade passage have been sampled periodically using a straight and a 90 degree triple-split fiber probe. Radial measurements at 39 radial stations were carried out at chosen axial positions in order to get the span-wise characteristics of the unsteady flow. Taking the experimental values of the unsteady flow velocities and turbulence properties, the effects of the rotor blade wake decay and secondary flow on the blade row spacing and stator passage flow at different operating conditions are discussed. For the normal operating point, the component of radial turbulent intensities in the leakage-flow mixing region is found to be much higher than the corresponding axial and tangential components. But for a higher value of the flow coefficient the relations are different.The results of the experiments show that triple-split fiber probes, straight and 90 degree measurements, combined with the ensemble average technique are a very useful method for the analysis of rotor flow in turbomachinery. Tip clearance vortex, secondary flow near the hub and radial flow in the wake, turbulent intensity and Reynolds stresses and also the decay of the rotor wakes can be obtained by this method.

This paper describes a Direct Carbon-Air Fuel Cell (DCFC) which uses a molten hydroxide electrolyte. In DCFCs, carbon is electrochemically directly oxidized to generate the power without a reforming process. Despite its compelling cost and performance advantages, the use of molten metal hydroxide electrolytes has been ignored by DCFC researches, primarily due to the potential lack of invariance of the molten hydroxide electrolyte caused by its reaction with carbon dioxide. This paper describes the electrochemistry of DCFC based on molten hydroxide electrolyte and discusses means to overcome the historical carbonate formation. Furthermore, it describes the cell performance during the initial stage of a long term operation and discusses the causes for the initial cell performance degradation. To date, five successive generations of medium temperature DCFC prototypes have been built and tested at SARA Inc. to demonstrate the technology, all using graphite rods as their fuel source. The basic feature of the cell is a simple design in which the cathode is not traditional gas fed electrode type. It is a non-porous electrode structure made of an inexpensive Fe-Ti alloy and gaseous oxygen is introduced into the cell by bubbling humid air through the electrolyte. The cell successfully demonstrated delivering more than 50 A at 0.3 V with the current density exceeding 100 mA/cm2. Main feature of DCFC with hydroxide electrolyte is that the cell performance decreases over time mainly due to oxygen cathode polarization. There are three possible causes for this performance decay: Carbonate formation, electrolyte evaporation due to air bubbling, and corrosion products build up. In order to determine the right cause for the performance decay a series of experiments was carried out investigating various parameters involving cell temperature, water content in the melt, current density, carbonate content in the melt, melt level in the cell, air flow rate and intermittent on-off operation. DCFC was operating at constant current while cell voltage and electrode potentials were recorded over time. Results obtained indicated that the performance of DCFC with hydroxide electrolyte during initial 200 h is governed by the oxygen cathode performance that is mainly affected by corrosion products. The corrosion products catalyze decomposition of peroxide ions which are reacting species at the cathode resulting in an increase of cathode polarization over time. Effect of carbonate ions on the initial cell performance decay is insignificant as compared to the effect of corrosion product. Means to overcome the corrosion products issue were discussed.

Objective: The objective of this research was to investigate the potential use of NMR for evaluating various internal quality factors of fruits and vegetables, leading to the eventual development of practical techniques that are useful for future development of NMR sensors. Summary: Investigation on NMR imaging, one-dimension NMR projection, and single-pulse free-induction-decay (FID) spectrum led to the development of high-speed NMR techniques for real-time sensing of internal quality of selected fruits. NMR imaging can be used for detecting internal defects and various quality factors such as bruises, dry regions, worm damage, stage of ripeness, tissue breakdown, and the presence of voids, seeds, sprouts, and pits. The one-dimension (1-D) image profile technique, in which the 1-D projection of the NMR signal of a selected slice of the intact fruit is recorded, is suitable for detecting tissue breakdown regions, presence of pits, and other defects in fruits. The oil and sugar content of fruits can be determined from the single-pulse FID spectrum measurement, in which a surface coil is used to acquire the FID spectrum and the ratio of the resonance peaks is used as the quality index. The latter two techniques are suitable for high-speed sorting of fruits. The most important accomplishment is the successful development of high-speed NMR techniques for determining internal quality of fruits while they are moving at speed up to 30 cm/s. This accomplishment is an important step toward the development of NMR techniques for on-line sorting of fruits and vegetables.

Several factors contribute to Surinames particular vulnerability to the effects of climate change. It is dependent on fossil fuels, has forests liable to decay, fragile ecosystems, and its low-lying coastal area accounts for 87% of the population and most of the countrys economic activity. Many sectors are at risk of suffering losses and damage caused by gradual changes and extreme events related to climate change. For Suriname to develop sustainably, it should incorporate climate change and its effects into its decision-making process based on scientific- evidence. The State of the Climate Report analyzes Surinames historical climate (1990-2014) and provides climate projections for three time horizons (2020-2044, 2045-2069, 2070-2094) through two emissions scenarios (intermediate/ SSP2-4.5 and severe/ SSP5-8.5). The analysis focuses on changes in sea level, temperature, precipitation, relative humidity, and winds for the seven subnational locations of Paramaribo, Albina, Bigi Pan MUMA, Brokopondo, Kwamalasamutu, Tafelberg Natural Reserve, and Upper Tapanahony. The Report also analyzes climate risk for the countrys ten districts by examining the factors which increase their exposure and vulnerability on the four most important sectors affected by climate change: infrastructure, agriculture, water, and forestry, as well as examining the effects across the sectors. The State of the Climate provides essential inputs for Suriname to develop and update its climate change policies and targets. These policies and targets should serve as enablers for an adequate mainstreaming of climate change adaptation and resilience enhancement into day-to-day government operations.