ModClark and Clark’s Unit Hydrograph (Clark’s UH) within HEC-HMS software are distributed and lumped models, respectively. Clark’s UH simulates the transformation and attenuation of excess precipitation, and requires time of concentration (Tc) and Storage Coefficient (R) parameters. ModClark transformation accounts for variations in travel time to catchment outlet from all regions of a catchment, and it additionally requires gridded representation of a catchment and Gridded cell-based input files. Four cases (three from observed rain, and one from radar reflectivity) of three chosen events were specifically chosen and examined for the comparison of simulation results with the same estimated initial parameters apart from different rainfall inputs. The Upper Waimakariri River Catchment was divided into ten subcatchments, and the HEC-HMS basin model parameters were estimated by using the physical/hydrological characteristics. However, ModClark transformation was unavailable because of an output error from converting ASCII to gridded Soil Conservation Service Curve Number (SCS CN) format by the conversion tool – ai2dssgrid.exe. Therefore, Mean Aerial Precipitation (MAP) for each subcatchment was calculated by Thiessen polygon method combined with an overlay analysis for grid-cell-based rainfall estimation from radar with geographic information system (GIS) tools. The automated calibration/optimisation procedure included in HEC-HMS package was applied to the cases which showed a deviation between simulation and observed flows. The purpose is to ‘optimise’ the initial estimates of parameters only in a mathematical-fit manner based on the observed flows from the only discharge gauge at Old Highway Bridge (OHB). The TC values calculated from the five equations vary in a relatively narrow range apart from the one from Bransby-Williams equation. Therefore, the values from all the other four equations were averaged and used as the initial TC input. The simulation results showed that there was a notable difference between observed and simulated hydrographs for some case studies even though TC, R, CN, and lag time were calibrated/optimised separately. Also, radar estimated rainfall and grid-based data storage system (DSS) need more investigations.

<p>This thesis report is focused on the growth of Pt/Mg multilayers and the studies of the sputter yield amplification effect in these. The main application is to use the multilayers as X-ray mirrors reflecting an X-ray wavelength of 17 Å. This wavelength is important for astronomical applications in general, and solar imaging applications in particular.</p><p>For periodic X-ray multilayer mirrors only a certain specific wavelength of X-rays can be reflected. What wavelength that is reflected depends on the individual layer thicknesses of the materials that are constituting the multilayer. These thicknesses can be determined using modified Bragg’s law and are approximately a quarter of the wavelength.</p><p>In order to obtain the exact desired layer thickness of each individual layer it is necessary to understand the growth processes and the effects that are going on during deposition of such multilayer mirrors. It has been shown that when depositing multilayers consisting of one very light and one very heavy material, like e.g. Pt and Mg, the deposition rate of the light element is non-linear with deposition time for thin layers. This is because of backscattered energetic neutrals from the heavy target material, which affects the growing film. Furthermore, a sputter yield amplification is present for thin layers when a light element is grown on top of a heavy element, i.e. for Mg on top of Pt.</p><p>Dual DC magnetron sputtering has been used to grow the Pt/Mg multilayers, and the influence of the backscattered energetic neutrals and the sputter yield amplification effect has been studied for Ar and Kr sputtering gases at pressures ranging from 3 up to 9 mTorr. The individual layer thicknesses have been obtained from simulations of hard X-ray reflectivity measurements using the IMD program. The number of backscattered energetic neutrals and their energies at the target have been calculated using the TRIM code.</p><p>Using the results obtained it is now possible to predict and compensate for the non-linear deposition rate of Mg.</p>

This thesis report is focused on the growth of Pt/Mg multilayers and the studies of the sputter yield amplification effect in these. The main application is to use the multilayers as X-ray mirrors reflecting an X-ray wavelength of 17 Å. This wavelength is important for astronomical applications in general, and solar imaging applications in particular. For periodic X-ray multilayer mirrors only a certain specific wavelength of X-rays can be reflected. What wavelength that is reflected depends on the individual layer thicknesses of the materials that are constituting the multilayer. These thicknesses can be determined using modified Bragg’s law and are approximately a quarter of the wavelength. In order to obtain the exact desired layer thickness of each individual layer it is necessary to understand the growth processes and the effects that are going on during deposition of such multilayer mirrors. It has been shown that when depositing multilayers consisting of one very light and one very heavy material, like e.g. Pt and Mg, the deposition rate of the light element is non-linear with deposition time for thin layers. This is because of backscattered energetic neutrals from the heavy target material, which affects the growing film. Furthermore, a sputter yield amplification is present for thin layers when a light element is grown on top of a heavy element, i.e. for Mg on top of Pt. Dual DC magnetron sputtering has been used to grow the Pt/Mg multilayers, and the influence of the backscattered energetic neutrals and the sputter yield amplification effect has been studied for Ar and Kr sputtering gases at pressures ranging from 3 up to 9 mTorr. The individual layer thicknesses have been obtained from simulations of hard X-ray reflectivity measurements using the IMD program. The number of backscattered energetic neutrals and their energies at the target have been calculated using the TRIM code. Using the results obtained it is now possible to predict and compensate for the non-linear deposition rate of Mg.

A fast and efficient method for the design of multi-layered circuit analog absorbing structures is developed. The method is based on optimization of specular reflection coefficient of a multi-layered absorbing structure comprising of lossy FSS layers by using Genetic Algorithm and circuit equivalent models of FSS layers. With the introduced method, two illustrative absorbing structures are designed with -15 dB reflectivity for normal incidence case in the frequency bands of 10-31 GHz and 5-46 GHz, respectively. To the author&rsquo / s knowledge, designed absorbers are superior in terms of frequency bandwidth to similar studies conducted so far in the literature. For broadband scattering characterization of periodic structures, numerical codes are developed. The introduced method is improved with the employment of developed FDTD codes to the proposed method. By taking the limitations regarding production facilities into consideration, a five-layered circuit analog absorber is designed and manufactured. It is shown that the manufactured structure is capable of 15 dB reflectivity minimization in a frequency band of 3.2-12 GHz for normal incidence case with an overall thickness of 14.2 mm.

Stereocomplex poly(methyl methacrylate) (PMMA) fibers for the purpose of reinforcing PMMA materials were developed. These kinds of composites are known as "self-reinforced" composites. We were successful in producing stereocomplex PMMA fibers with three different methods - wet spinning, gel spinning and electrospinning. Gel spinning and electrospinning produced the most crystalline fibers. Steroecomplex PMMA fibers were further shown to be resistant to high temperature and also to hot monomer solvent during bulk polymerization. We further describe our efforts in characterization, replication and mimicry of structural color features of butterflies and beetles. We have developed a simple method of characterizing the bidirectional reflectance distribution function of microscopic objects such as butterfly wing scales. We used this method to characterize nanometer sized structural color features resulting from the replication of butterfly Morpho rhetenor, mimickry of butterfly Papilio palinurus and also the native structural color features of iridescent beetle Chrysina gloriosa, which were shown to be cholesteric focal conic defects lined on the surface.

Η εργασία αυτή περιγράφει αναλυτικά την κατασκευή και αξιολόγηση πειραματικής διάταξης ανακλαστικότητας ακτίνων-Χ, που πραγματοποιήθηκε στο Εργαστήριο Φυσικής Στερεάς Κατάστασης του τμήματος Φυσικής του Πανεπιστημίου Πατρών. Με τη βοήθεια αυτής της πειραματικής διάταξης θα είναι εύκολος ο καθορισμός των χαρακτηριστικών ιδιοτήτων επιφανειών καθώς επίσης και η μελέτη υμενίων τα οποία έχουν προσροφηθεί σε υποστρώματα. Στο πρώτο κεφάλαιο της εργασίας παρουσιάζονται οι βασικές σχέσεις υπολογισμού της ανακλαστικότητας καθώς και η μέθοδος ανάλυσης των πειραματικών αποτελεσμάτων. Στο επόμενο κεφάλαιο παρουσιάζονται αναλυτικά όλα τα βήματα που πραγματοποιήθηκαν για την κατασκευή της πειραματικής διάταξης. Στο κεφάλαιο αυτό περιγράφονται όλα τα μηχανικά μέρη του φασματόμετρου καθώς και οι απαιτούμενες ρυθμίσεις που πραγματοποιήθηκαν προκειμένου να εξασφαλιστεί η σωστή λειτουργία του. Με λήψη ενός φάσματος από ένα δείγμα πυριτίου και τον προσδιορισμό των γωνιών Bragg αποδείχθηκε η σωστή λειτουργία του γωνιομέτρου. Το επόμενο βήμα ήταν ο υπολογισμός της διακριτικής ικανότητας της συσκευής. Με υπολογιστικό πρόγραμμα [Ν. Κάτσενου Διπλωματική Εργασία] το οποίο λαμβάνει υπόψη του όλη την γεωμετρία της διάταξης υπολογίστηκε η διακριτική ικανότητα της συσκευής. Η τιμή της είναι 0.0120 και είναι σταθερή για τις γωνίες από 0.20 έως 1.60. Προκειμένου να βελτιωθεί η τιμή της διακριτικής ικανότητας είναι απαραίτητο να χρησιμοποιηθούν πολύ λεπτές σχισμές τόσο στη λυχνία όσο και στον απαριθμητή. Επιπροσθέτως κατασκευάστηκε ειδική διάταξη, “μαχαίρι”, το οποίο στηρίζεται στην βάση του δείγματος και όπως διαπιστώθηκε βελτιώνει την διακριτική ικανότητα της διάταξης και μειώνει το υπόστρωμα.. Ως τελευταίο βήμα ήταν ο υπολογισμός του υποστρώματος και η διόρθωσή του. Στο δεύτερο κεφάλαιο περιγράφεται αναλυτικά η διαδικασία διόρθωσης του υποστρώματος σε ένα φάσμα ανακλαστικότητας. Στην συνέχεια παρουσιάζονται πειραματικές μετρήσεις από διάφορα δείγματα. Σε όλα τα δείγματα χρησιμοποιήθηκε ως υπόστρωμα πυρίτιο. Στα περισσότερα από αυτά προσροφήθηκε, με την μέθοδο επίστρωσης με περιστροφή του υποστρώματος, πολυστηρένιο. Χρησιμοποιήθηκαν διάφορες συγκεντρώσεις διαλύματος πολυστηρενίου σε τολουόλιο προκειμένου να δημιουργηθούν δείγματα με διαφορετικά πάχη. Επίσης με την μέθοδο της εξάχνωσης εναποτέθηκε υμένιο αλουμινίου σε υπόστρωμα πυριτίου. Από τις πειραματικές μετρήσεις που προέκυψαν για την ανακλαστικότητα προκύπτει ότι η κρίσιμη γωνία ανάκλασης είναι 0.220 ενώ για γωνίες μεγαλύτερες από αυτή η ανακλαστικότητα αρχίζει και μειώνεται απότομα. Μέχρι την γωνία 2.00 η τιμή της ανακλαστικότητας μειώνεται περίπου έξι τάξεις μεγέθους. Χρησιμοποιώντας τις πειραματικές μετρήσεις που πήραμε μπορούμε να εξάγουμε πληροφορίες για το πάχος, την πυκνότητα και την τραχύτητα των επιφανειών που μελετάμε. Διαπιστώθηκε λοιπόν ότι η συσκευή λειτουργεί ικανοποιητικά. Βελτιώσεις που μπορούν να γίνουν αφορούν: α) Την κατασκευή θαλάμου κενού εντός του οποίου θα ευρίσκεται το δείγμα. Η βελτίωση αυτή θα επιτρέψει να λαμβάνονται φάσματα ανακλαστικότητας με πολύ χαμηλό υπόστρωμα. Με τον τρόπο αυτό θα βελτιωθεί η ποιότητα των φασμάτων για γωνίες ανάκλασης μεγαλύτερες από 1.20 γεγονός που θα δώσει πιο σαφής πληροφορίες για τη δομή πολύ λεπτών υμενίων. β) Μακροπρόθεσμα θα τοποθετηθεί στη συσκευή σύστημα παραλληλισμού της δέσμης το οποίο θα αυξήσει την ένταση της προσπίπτουσας ακτινοβολίας στο δείγμα. Με τον τρόπο αυτό θα ελαττωθεί ο χρόνος λήψης του συνολικού φάσματος ενώ ταυτόχρονα θα βελτιωθεί η στατιστική ιδιαίτερα στις μεγάλες γωνίες σκέδασης και θα καταστεί έτσι άνετη η μελέτη εξαιρετικά λεπτών υμενίων (μικρότερα των 20Å). / -

The reflectivity spectrum of SbSeI crystals in the spectral range of 10 – 300 cm–1 over a wide range of temperatures (10 – 297 K) with light polarization E||c and Ec was experimentally studied. Measurements were carried out in Germany. Also experimental research was carried out with the reflectivity spectrum of SbSI crystals in the spectral range of 10-450 cm–1 with light polarization E||c over temperature range (273 – 350 K) . The spectra of optical constants and optical functions were calculated using the Kramers–Kronig (KK) technique and the method of optical parameter fitting (OP). Tables and diagrams are presented. Vibrational spectra of SbSeI crystals in harmonic approximation were theoretically investigated. The oscillation frequencies of normal vibrational modes and the amplitudes of normal coordinates along z(c) axis and in x-y plane by diagonalization of the dynamic matrix were calculated. Experimental studies of reflectivity spectrum of SbSeI crystals revealed, that there is no ferroelectric phase transition in SbSeI crystals in the temperature range of 10 - 297 K. And experimental studies of reflectivity spectrum of SbSeI crystals proved, that ferroelectric phase transition in SbSI crystals grown by us occurs at temperature TC = 293 K. SbSI crystals in range of temperatures T > TC are in paraelectric phase, and in range of temperatures T < TC are in ferroelectric phase. It was experimentally proved, that low-frequency IR mode of SbSeI, when E ׀׀ c is... [to full text]

Ce travail de thèse porte sur l’étude des propriétés optiques et électroniques des puits quantiques de GaN / AlGaN grâce à des techniques classiques de réflectivité résolue en angle et de photoluminescence, ainsi qu’avec la technique de photoluminescence résolue temporellement. Les expériences de photoluminescence en régime continu ont permis d’estimer les énergies des transitions excitoniques qui sont également accessibles en réflectivité. Ces techniques ont ainsi permis de mettre en évidence l’effet Stark dans les puits quantiques GaN / AlGaN. L’effet Stark sur les énergies de transition est cohérent avec la théorie des fonctions enveloppes. Les spectres de réflectivité permettent d’accéder à la force d’oscillateur des excitons grâce à leur modélisation par le formalisme des matrices de transfert, prenant en compte les phénomènes d’élargissement homogène et inhomogènes des transitions optiques. Enfin, les mesures de photoluminescence résolue en temps en fonction de la température, ont également permis d’extraire la force d’oscillateur qui est inversement proportionnelle au temps de recombinaison radiative. Cette étude a également permis de mettre en évidence l’effet Stark responsable de la diminution de la force d’oscillateur en fonction de l’épaisseur du puits quantique mais aussi en fonction de la composition d’aluminium. L’augmentation de l’épaisseur du puits entraîne une diminution du recouvrement des fonctions d’onde, et une augmentation de la composition d’aluminium intensifie le champ électrique et diminue également le recouvrement des fonctions d’onde. / This work deals with the study of optical and electronic properties of GaN / AlGaN quantum wells, by classical techniques of spectroscopy including angle resolved reflectivity or photoluminescence, but also by time resolved photoluminescence. The continuous wave photoluminescence experiments allowed estimating the energies of the excitonic transitions, which are also available through reflectivity. These techniques highlighted the Stark effect in GaN / AlGaN quantum wells. The influence of the Stark effect on the energies of the excitonic transitions is well reproduced by envelop functions theory. Reflectivity spectra give access to the oscillator strength via their fitting by transfer matrix formalism, taking in account both homogeneous and inhomogeneous broadenings of the optical transitions. Finally, time resolved photoluminescence measurements as a function of temperature were performed to extract the oscillator strength, which is proportional to the inverse of the radiative recombination time. This technique also highlighted the Stark effect which is responsible of the vanishing of the oscillator strength with the thickness of the well and the aluminium composition. Increasing of the quantum well’s thickness induces decreasing of wave functions overlap, as well as an increasing of the aluminium composition which intensifies the electric field and splits the wave functions.

No description available.

In order to understand the properties of thin film devices, knowledge of the material's structure is essential. The work presented here combines magnetic and structural characterization of the systems studied to gain a deeper physical understanding. The magnetic properties have been studied with a combination of x-ray magnetic circular dichroism, SQUID magnetometry and magneto-optical Kerr effect. For the structural characterization, x-ray reflectivity and diffraction have been used, complemented by neutron diffraction and transmission electron microscopy. One structural property that affects the magnetic moment in metal-on-metal superlattices is interdiffusion between the layers. This is discussed for bcc Fe/Co(001) and bcc Fe81Ni19/Co(001) superlattices. The effect of interdiffusion was seen as a large region of enhanced magnetic moments as compared to theoretical calculations, which assume perfectly sharp interfaces. For the Fe81Ni19/Co(001) superlattices the chemical interface region, as revealed by neutron diffraction, was in good agreement with the region of magnetic enhancement. Another structural property that has been investigated is the strain in the magnetic layers. This does not affect the spin magnetic moment to a large extent. However the magnetocrystalline anisotropy and the orbital moment are affected by the presence of strain. The effects on the orbital moment from strain and interfaces for Fe in Fe/V superlattices was studied, and it was found that the two contributions were separable. In this context the effect of strain on the out-of-plane magnetocrystalline anisotropy in FeCo/Pt has also been studied. The latter system is interesting from a technological perspective since tetragonally distorted FeCo alloys have the potential to be suitable new materials in computer hard drives. Finally, a computer program, based on the Differential Evolution algorithm, to refine primarily x-ray reflectivity data, is presented.