In pursuit of negatively associated measures, this thesis focuses on certain negative correlation properties in matroids. In particular, the results presented contribute to the search for matroids which satisfy $$P(\{X:e,f\in X\}) \leq P(\{X:e\in X\})P(\{X:f\in X\})$$ for certain measures, $P$, on the ground set. Let $\mathcal M$ be a matroid. Let $(y_g:g\in E)$ be a weighting of the ground set and let $${Z = \sum_{X}\left( \prod_{x\in X} y_x\right) }$$ be the polynomial which generates Z-sets, were Z $\in \{$ B,I,S $\}$. For each of these, the sum is over bases, independent sets and spanning sets, respectively. Let $e$ and $f$ be distinct elements of $E$ and let $Z_e$ indicate partial derivative. Then $\mathcal M$ is Z-Rayleigh if $Z_eZ_f-ZZ_{ef}\geq 0$ for every positive evaluation of the $y_g$s. The known elementary results for the B, I and S-Rayleigh properties and two special cases called negative correlation and balance are proved. Furthermore, several new results are discussed. In particular, if a matroid is binary on at most nine elements or paving or rank three, then it is I-Rayleigh if it is B-Rayleigh. Sparse paving matroids are B-Rayleigh. The I-Rayleigh difference for graphs on at most seven vertices is a sum of monomials times squares of polynomials and this same special form holds for all series parallel graphs.

This thesis describes a method developed to quickly measure the Rayleigh wave Q for a test material using a minimally invasive laser probe. The probe was donated to our lab by Dr. Alex Maznev at Phillips AMS in Natick, Ma. The machine was originally used to measure ultra thin film metal thicknesses; however we have utilized it to suit our needs. The optics head relies on a technique known as the transient grating method to generate a dispersion curve. This dispersion curve is then operated on by a local approximation for the Kramers-Kronig relations. The Kramers-Kronig relations for acoustic waves relate the real and imaginary parts of the dynamic compressibility to one another. The real part of the compressibility relates to the phase velocity of the wave and the imaginary part relates to the attenuation. Once the attenuation for the corresponding range of frequencies is determined the last step is to apply both the dispersion data and the attenuation data to the material Q equation to find Q over a range of frequencies. This thesis discusses the design of the machine, the theory behind the Kramers-Kronig relations and surface acoustic waves, the experimental procedure, and lastly results generated by the technique.

The cooling problem has become a serious subject in order to keep away from malfunctioning for a high performance and miniaturized electronic component. For instance, the monitor backlight LED must be cooled adequately. In this thesis, a natural convection cooling problem for the vertical channel with equally spaced heating blocks on one wall is studied by a numerical modeling to simulate a monitor backlight LED cooling. A control volume method is employed for the numerical modeling. The results of heat transfer coefficients and hot spots for various channel gap, LED spacing and Rayleigh number are presented. This study can provide design reference for related cooling problems.

This work describes the development of a Raman spectroscopy system for measuring aerothermochemistry in high-speed jets and flames. A transmissive grating spectrometer was newly developed for capturing pure rotational Raman and rotationalvibrational Raman with a single CCD camera. Previous state-of-the-art experiments applied line imagining in known flowfields of constant pressure. The system described herein is designed to provide local measurement of pressure, with full thermochemistry, along a line. In every point, temperature will be measured by examining the Boltzmann decay of the rotational spectrum, while molar fraction will be measured from the vibrational Raman spectrum. The temperature and concentrations will then be combined to obtain partial pressure measurements via the equation of state. This work examines the phenomenology of rotational and vibrational Raman scattering and proposes algorithms that can be used for data extraction.

The effect of single mode initial conditions at the interface of Rayleigh-Taylor(RT) mixing are experimentally examined utilizing the low Atwood number water channel facility at Texas A&M. The water channel convects two separated stratified flows and unifies them at the end of a splitter plate. The RT instability is attained by convecting a cold stream above a warmer stream. Average density calculations are based on long time average optical measurements. The water channel was modifified with a flapper fin like device at the end of the splitter plate which was actuated by a computer controlled servo motor. Other modifications to the experiment were implemented resulting in reduced uncertainty. The experiment examined five different modes in addition to the baseline: 2 cm, 3 cm, 4 cm, 6 cm, and 8 cm wavelengths. The mixing width growth rates were shown to be dependent on initial conditions. Additionally, it appears that the growth rates commence with terminal velocity and are observed to line up with the baseline case.

Abstract The first hyperpolarizability(£]) of five charge-transfer molecules are determined using the hyper-Rayleigh scattering (HRS) technique at two excitation wavelengths : 1064nm and 1907nm. The 1064nm excitation wavelength is derived from a Nd: YAG pulsed laser, and the 1907nm excitation wavelength is obtained by shifting the 1064nm laser light by stimulated Raman scattering of pressurized H2 gas. Four of the five samples contains thiophene and thiazole are synthetized by Prof. Shu Ching-Fong at the National Chiao Tung University (NCTU) and the other sample is synthetized by Prof. Hong, Jin-Long at the National Sun Yat-sen University (NSYSU). The measured £] values are used to calculate the intrinsic molecular hyperpolarizabilities using the two-level model previously developed by Oudar and Chemla. The results are related to molecular structure.

The technique of hyper-Rayleigh scattering is employed to measure the first molecular hyperpolarizabilities£]of nonlinear optical chromophores provided by Industrial Technology Research Institute. £]0. In the thesis, the effect of the molecular structure and the solvent on the hyperpolarizabilities will be discussed further.

Nous avons modélisé numériquement la stabilité d'un système de deux couches d'un même fluide pur supercritique soumis à une différence de température initiale à l'interface. La grande compressibilité et la faible diffusivité thermique des fluides critiques entraînent une instabilité gravitationnelle de type Rayleigh-Taylor de la couche de diffusion. Cette instabilité est similaire à celle que l'on retrouve dans le cas de deux fluides miscibles à condition de remplacer le coefficient de diffusion moléculaire par celui de la diffusion thermique. Nos résultats numériques semblent être consistants, d'un point de vue de la relation de dispersion dans le cas linéaire, avec ceux de Duff et al. [Duf62] considérés dans le cas de deux fluides miscibles. Nous avons aussi montré que, lorsque l'épaisseur de la couche inférieure devient plus petite que l'épaisseur de la couche de diffusion thermique basée sur le taux de croissance maximal alors le système devenait stable. Un diagramme de stabilité a été établi en fonction de trois paramètres: l'épaisseur de la couche inférieure, la différence de densité entre les deux couches et la distance au point critique. Lorsque l'on s'approche du point critique, la stratification devient de plus importante (à cause de la forte compressibilité) et tend à stabiliser la configuration. Par ailleurs, le filtrage acoustique initialement utilisé afin de réduire les coûts de calcul, ne s'est pas avéré nécessaire puisque la méthode des volumes finis est naturellement filtrante (formulation intégrale ou variationnelle des équations).

ITC/USA 2014 Conference Proceedings / The Fiftieth Annual International Telemetering Conference and Technical Exhibition / October 20-23, 2014 / Town and Country Resort & Convention Center, San Diego, CA / Spatial modulation (SM) is a transmission scheme where only one transmit antenna is active at any time instant. It thus reduces interchannel interference (ICI) and receiver complexity over traditional multi-antenna systems. However, the spectral efficiency of SM is low. To improve the spectral efficiency, generalized spatial modulation (GSM) can be used. In this paper, we propose to apply the Alamouti technique with GSM for correlated antennas, and show that the proposed approach provides significant improvement over conventional SM and GSM. Our study also shows the importance of bit-to-antenna mappings and their roles on the selection of appropriate correlated antennas.

Σε αυτή τη διπλωματική εργασία γίνεται μελέτη του φαινομένου των διαλείψεων. Στα κεφάλαια 1 έως 3 γίνεται θεωρητική μελέτη και περιγραφή των διαλειπτικών φαινομένων. Συγκεκριμένα, πρώτο στο κεφάλαιο γίνεται σύντομη αναφορά των θεμάτων που αναλύονται στα επόμενα κεφάλαια. Στο δεύτερο κεφάλαιο γίνεται ανάλυση των μηχανισμών ηλεκτρομαγνητικής μετάδοσης και δίνεται μια εικόνα των επιδράσεων των μηχανισμών αυτών στο λαμβανόμενο σήμα και αναλύεται ο τρόπος δημιουργίας των διαλείψεων. Στο τρίτο κεφάλαιο αναλύονται οι τρόποι επίδρασης των διαλειπτικών φαινομένων στο ασυρματικό κανάλι και αναφέρονται τρόποι υπολογισμού των επιδράσεων αυτών. Στο τέταρτο κεφάλαιο αναλύονται τα φαινόμενα fading σε κανάλια εσωτερικού χώρου , δίνονται κατάλληλες κατανομές fading για την περιγραφή τέτοιων καναλιών καθώς και μέθοδοι υπολογισμού των επιπτώσεών τους . Στο πέμπτο κεφάλαιο αναλύονται τα φαινόμενα fading σε κανάλια εξωτερικού χώρου δίνονται κατάλληλες κατανομές fading για την περιγραφή τέτοιων καναλιών καθώς και μέτρα επίδοσης για τις συγκεκριμένες κατανομές. Στο έκτο κεφάλαιο αναφέρονται πειραματικές μέθοδοι μέτρησης των διαλειπτικών φαινομένων για κανάλια εξωτερικού χώρου, για κανάλια εξωτερικού χώρου και για σύνθετα κανάλια εξωτερικού/εσωτερικού χώρου, και γίνεται σύγκριση των πειραματικών και θεωρητικών τιμών. Στο έβδομο κεφάλαιο γίνεται προσομοίωση σε περιβάλλον MatLab και συγκρίνονται τα αποτελέσματα των προσομοιώσεων με τις θεωρητικές τιμές για αδιαμόρφωτο φορέα και για τις κυριότερες διαλειπτικές κατανομές. Στο τέλος της εργασίας γίνεται σύντομη σύγκριση των μεθόδων προσομοίωσης με τις πειραματικές μεθόδους και αναφέρονται οι πιθανοί λόγοι απόκλισης των τιμών από την θεωρητική ανάλυση. / In this work the fading phenomenon is studied. In chapters 1, 2 and 3 fading channels are described theoretically. In chapters 4 and 5 are given suitable fading distributions and perfomance mesures for indoor and outdoor channels respectively. In chapter 6 are described experimental procedures for the study of the fading effects. Chapter 7 deals with simulation methods of fading channels and at the end the results of experimental procedures are compared to these of simulation methods.