Thesis advisor: Pradip Bakshi / This thesis is a theoretical study of the electron transport and response properties of epitaxially grown, low-dimensional semiconductor quantum well heterostructures, under steady-state, current driven (nonequilibrium) conditions. These structures operate in the Terahertz (THz) frequency and submillimeter wavelength range, and are the leading candidates for compact, coherent sources of THz radiation. This work is divided into two parts: Part I consists of an analytical study of the individual quantum well units, and the tunneling transmission characteristics, for which reasonably accurate algebraic expressions are obtained. An underlying philosophy of this work is the desire to describe each of the key components involved, independently, through these simple analytical expressions. In Part II the numerical study of the transport and radiation response of the quantum well structures specially designed to generate THz radiation based on the plasma instability concept is presented. Several models are proposed which describe the overall electron transport and which determine the underlying nonequilibrium steady state. In particular, the key features of the experimental current-voltage (IV) curves for such structures are explained, and the corresponding response properties are determined. The modeling and simulation of these potential optoelectronic devices is a crucial tool for elucidating the precise mechanisms and interplay of the many microscopic processes which give rise to the observed behavior. Key features of the radiation response arise from the intersubband plasma instability which occurs due to the resonant interaction of an emission and an absorption mode, and these features are compared with the experimental observations. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / An X-ray diffraction study of tri-(p-aminophenyl) carbonium perchlorate, (H2NC6H4)3C.ClO4, was carried out in order to determine (1) the effects of substituents on the structure of triphenylcarbonium ion, and (2) the effect of crystal symmetry on the configuration of the triarylcarbonium ions. [TRUNCATED] / 2031-01-01

Les hétéropolyanions (HPA) possèdent des propriétés acidobasiques et rédox remarquables qui en font des composés particulièrement attractifs en catalyse. Ces HPA peuvent subir une modification de leur degré de réduction au cours de la réaction catalytique, ils peuvent également être utilisés directement à l’état réduit pour augmenter leurs performances. Dans ce contexte, ce travail présente diverses voies de synthèse permettant le contrôle de l’état de réduction d’hétéropolyanions issus des acides H4SiMo12O40 et H3PMo12O40 de structure de Keggin. Les HPA réduits à 2 et 4 électrons ont pu être obtenus en solution et sous forme de sels, par utilisation d’agents réducteurs comme MoCl3, N2H4 et NaBH4 ou par électrolyse à potentiel imposé. L’emploi d’agents réducteurs métalliques comme l’étain et le titane a également permis d’isoler de nouveaux composés réduits incorporant Sn et Ti au sein de leurs structures. Une étude de ces espèces en solution et à l’état solide montre qu’un contrôle cinétique de la réduction favorise l’obtention d’espèces « substituées » où le métal réducteur remplace 1 ou 2 atomes de molybdène dans la structure. En revanche, des conditions thermodynamiquement plus « dures » induisent la formation d’entités où les atomes Sn et Ti viennent « caper » l’hétéropolyanion. Deux nouvelles structures « monocapée » ((IV)α[SiMo12O40Sn(OH2)2]4-, (TBA+)4) et « bicapée » ((IV)α[SiMo12O40(SnO)2]4-, (TBA+)4) ont ainsi pu être caractérisées par diffraction de rayon X sur monocristal. Une ouverture en catalyse d’HDS est également proposée, mettant en évidence une meilleure sulfuration des espèces réduites en particulier pour les composés « capés ». / Heteropolyanions (HPA) have remarkable acidobasic and redox properties, which made of them attractive catalytic compounds. HPA can modify their sareduced states during catalytic processes, they also can be used to improve catalytic performances. In this context, this work presents various ways of reduced heteropolyanions synthesis descended from H4SiMo12O40 and H3PMo12O40 Keggin acids, allowing a reduction state control. 2 and 4 electrons reduced HPA’s have been obtained in solution or as various salts, by using reducing agents as MoCl3, H2N-NH2 and NaBH4 or electrolysis. New reduced compounds incorporating Sn or Ti in their structures have been isolated using metallic reducing agent like tin or titanium. Solution and solid state studies show that kinetic control of the reaction facilitates substituted species formation, in which one tin or titanium atoms can replace molybdenium atoms. In contrast, harder thermodynamic reactions conditions induce the formation of tin or titanium capped compounds. 2 news mono capped ((IV)α[SiMo12O40Sn(OH2)2]4-, (TBA+)4 ) and bi capped ((IV)α[SiMo12O40(SnO)2]4-, (TBA+)4 ) structures have been described by mono cristal DRX. A catalytic opening HDS study is also proposed, showing a best sulfuration of the pre reduced species, particularly capped species.

The contemporary world challenges many traditional notions about the nature of organizations (Neher, 1997). Today, organizational structures with more complicated communication have appeared, such as "networks" and "virtual organizations." New technology brought about these changes by overcoming limited resources and locations. Without instantaneous computerized communication, complicated global organizations could not exist. The relationship between organizational structures and new technology has been of primary importance for managers designing hierarchical structures. Organizations must continue to meet the challenge of incorporating new technology into their companies. In this study, twenty employees from Fortune 500 companies were selected to participate in pre-questionnaires and telephone interviews. The data was summarized into eleven categories focusing on three research questions: Employee perceptions of reengineering organizations, adoption of new information communication technology, and the relationship between technology and organizational structure. The findings revealed more complicated communication occurring within organizations reflected through the adoption of information communication technology. Although information flow in most organizations remained vertical from top down, upper level managers were able to bypass mid-level managers and communicate directly with employees and vice versa. This showed the emergence of new organizations featuring less hierarchical structures.

The search for antifungal secondary metabolites from cruciferous plants exhibiting resistance to pathogenic fungi led to the investigation of <i>Eruca sativa </i>(rocket). Chemical analysis of extracts showed arvelexin (51) as the only inducible component. Bioassay guided isolation (FCC, PTLC) and characterization (NMR, MS) led to the identification of two phytoanticipins, 4-methylthiobutyl isothiocyanate (166) and bis(4-isothiocyanatobutyl)disulfide (167). Compounds 166 and 167 inhibited the germination of spores of <i>Cladosporium cucumerinum</i> in TLC biodetection assays.<p>Next, isotopically labeled compounds containing 2H and 34S at specific sites were synthesized for use in studying of the biosynthetic pathway of crucifer phytoalexins and indolyl glucosinolates. Among the synthesized precursors, [4',5',6',7'-2H4]indolyl-3-[34S]acetothiohydroxamic acid (174a), the first sulfur-34 containing indolyl derivative was synthesized. In addition, non-isotopically labeled compounds (containing 1-methyl, 1-boc and 1-acetyl groups), that is, substrates used for precursor-directed biosynthesis, were also prepared.<p>With the precursors in hand, the biosynthetic pathway(s) and biogenetic relationship between phytoalexins was investigated using the tuberous crucifers, <i>Brassica napus </i> L. ssp rapifera (rutabaga) and <i>B. rapa </i> (turnip), and detached leaves of <i>Erucastrum gallicum </i> (dog mustard). The biosynthetic relationship between indolyl glucosinolates and phytoalexins was investigated in rutabaga and turnip. The indolyl moiety of the phytoalexins cyclobrassinin (28), rutalexin (33), spirobrassinin (34), brassicanate A (43), and rapalexin A (53), as well as indolyl glucosinolates glucobrassicin (70), 4-methoxyglucobrassicin (156), and neoglucobrassicin (199) was confirmed to derive from L-tryptophan (78). The 1-methoxy-containing phytoalexins, erucalexin (38) and 1-methoxyspirobrassinin (35) were shown to derive from indolyl-3-acetaldoxime (112) through 1-methoxyindolyl-3-acetaldoxime (116). The 1-methoxy substituent of neoglucobrassicin was also shown to derive from 1-methoxyindolyl-3-acetaldoxime (116).<p>The incorporation of indolyl-3-acetothiohydroxamic acid (174) into the phytoalexins cyclobrassinin, rutalexin, brassicanate A, rapalexin A, and spirobrassinin, and into the glucosinolate glucobrassicin is reported for the first time. On the other hand, incorporation of 174 into 4-methoxyglucobrassicin and neoglucobrassicin was not detected under current experimental conditions. Cyclobrassinin was incorporated into spirobrassinin among the NH-containing phytoalexins, whereas sinalbin B (31) [biosynthesized from 1-methoxybrassinin (18)] was incorporated into erucalexin and 1-methoxyspirobrassinin. The efficient metabolism of [SC2H3]brassicanal A into [SC2H3]brassicanate A suggested a biogenetic relationship between these two phytoalexins, whereas absence of incorporation of indolyl-3-acetonitrile (49) into rutabaga phytoalexins or indolyl glucosinolates indicated that 49 is not a precursor of these secondary metabolites under the current experimental conditions.<p>The rutabaga and turnip tubers separately metabolized 1-methylindolyl-3-acetaldoxime (170) and 1-methylindolyl-3-acetothiohydroxamic acid (178) into 1-methylglucobrassicin (201); however, no 1-methyl-containing phytoalexins were detected in the extracts. Rutabaga tissues metabolized 1-(tert-butoxycarbonyl)indolyl-3-methylisothiocyanate (180) into 1-(tert-butoxycarbonyl)brassinin (181) and 1-(tert-butoxycarbonyl)spirobrassinin (196), whereas 1-acetylbrassinin (184) was the only detectable metabolic product of 1-acetylindolyl-3-methylisothiocyanate (183) in both rutabaga and turnip root tissues.<p>In conclusion, indolyl-3-acetothiohydroxamic acid (174) seems to be the branching point between brassinin and glucobrassicin. The biosynthetic pathway of NH-containing crucifer phytoalexins was mapped and follows the sequence L-tryptophan, indolyl-3-acetaldoxime, indolyl-3-acetothiohydroxamic acid, brassinin (possibly through indolyl-3-methylisothiocyanate), and other phytoalexins. The biosynthetic pathway of 1-methoxy-containing phytoalexins follows a similar sequence through 1-methoxyindolyl-3-acetaldoxime (biosynthesized from indolyl-3-acetaldoxime).

There is evidence for the existence of non-classical bonding in several binary antimonides, selenides, and tellurides. Owing to such non-classical bonding, some of these solid materials exhibit exciting semiconducting and thermoelectric properties, which make them attractive from a technological view point. However, lack of efficiency is a serious limitation in most of those thermoelectrics. It is very crucial, hence, to find new materials with superior properties and understand the structure and bonding in such materials, in order to facilitate the fine-tuning of the physical properties. With this expectation, several quaternary barium copper chalcogenides are synthesized and characterized in the present study. The chalcogen elements, selenium tellurium, are used in various ratios, in order to understand and tune the binding interactions. Extensive single crystal x-ray diffraction studies are expected to reveal the minute details of the bonding interactions together with electronic structure calculation and physical property measurements. In addition, characterization techniques such as powder x-ray diffraction, electron microscopy, differential scanning calorimetry, thermopower and conductivity measurements are utilized. The ternary and quaternary chalcogenides, Ba₂Cu₄₋ₓSeyTe₅₋y were synthesized from the elements in stoichiometric ratios at 700°C, followed by annealing at 600°C. The ternary telluride Ba₂Cu₄₋ₓTe₅ crystallizes in a new structure type, space group C2/c, with lattice dimensions of a = 9.4428(6) Å, b = 9.3289(6) Å, c = 13.3028(8) Å, β = 101.635(1)°, V = 1147.8(1) Å3, for x = 0.75(1) (Z = 4). The corresponding selenide-telluride adopts another new, but strongly related, structure type, space group P4₁2₁2, with a = 6.5418(3) Å, c = 25.782(2) Å, V = 1103.3(1) Å3, for Ba₂Cu₃.₂₆₍₂₎Se₀.₇₂₉₍₈₎Te₄.₂₇₁ (Z = 4). Between 0.13 and 1.0 Te per formula unit can be replaced with Se, while the Cu content appears to vary only within 0.67 ≤ x ≤ 0.81 for Ba₂Cu₄₋ₓSeyTe₅₋y. Despite crystallizing in different crystal systems, the telluride and the selenide-telluride exhibit topologically equivalent structure motifs, namely chains of Cu(Se,Te)₄ tetrahedra with a Cu atom cis/trans chain as well as an almost linear Te atom chain. All these chalcogenides - as far as measured - are p-doped semiconductors, as determined by Seebeck coefficient and electrical conductivity measurements. Two new orthorhombic chalcogenides, Ba₂Cu₆₋ₓSeyTe₅₋y and Ba₂Cu₆₋ₓSyTe₅₋y were synthesized at 800°C. They are isostructural and crystallize in a new structure type, with space group Pbam. Ba₂Cu₆₋ₓSyTe₅₋y, with a = 9.6560(6) Å, b = 14.0533(9) Å, c = 4.3524(3) Å and Ba₂Cu₅.₆₄Se₁.₀₉Te₃.₉₁with a = 9.7048(6) Å, b = 14.1853(9) Å, c = 4.3840(3) Å. They have Cu6 units extending along c-axis, and two such units are interconnected by S or Se atoms along a-axis. These compounds are nonmetallic with low Seebeck coefficients. Two more new quaternary chalcogenides were uncovered, BaCu₅.₉₂₆₍₁₅₎SeTe₆ and BaCu₅.₇₂₍₁₆₎Se₀.₄₆₄₍₁₅₎Te₆.₅₃₆ with a = 6.9680(2) Å and a = 6.9888(4) Å, respectively, in space group Pm̅3. These compounds have basic Cu₈Te₁₂ frameworks, which can be an important feature for thermoelectric materials. Ba occupies the void. One Cu atom from each cage cluster of eight such cages forms a Cu₈ cube with Se atom occupying it. BaCu₅.₉SeTe₆ was experimentally determined to be p-type doped semiconductor with moderate Seebeck coefficient value.

The search for antifungal secondary metabolites from cruciferous plants exhibiting resistance to pathogenic fungi led to the investigation of <i>Eruca sativa </i>(rocket). Chemical analysis of extracts showed arvelexin (51) as the only inducible component. Bioassay guided isolation (FCC, PTLC) and characterization (NMR, MS) led to the identification of two phytoanticipins, 4-methylthiobutyl isothiocyanate (166) and bis(4-isothiocyanatobutyl)disulfide (167). Compounds 166 and 167 inhibited the germination of spores of <i>Cladosporium cucumerinum</i> in TLC biodetection assays.<p>Next, isotopically labeled compounds containing 2H and 34S at specific sites were synthesized for use in studying of the biosynthetic pathway of crucifer phytoalexins and indolyl glucosinolates. Among the synthesized precursors, [4',5',6',7'-2H4]indolyl-3-[34S]acetothiohydroxamic acid (174a), the first sulfur-34 containing indolyl derivative was synthesized. In addition, non-isotopically labeled compounds (containing 1-methyl, 1-boc and 1-acetyl groups), that is, substrates used for precursor-directed biosynthesis, were also prepared.<p>With the precursors in hand, the biosynthetic pathway(s) and biogenetic relationship between phytoalexins was investigated using the tuberous crucifers, <i>Brassica napus </i> L. ssp rapifera (rutabaga) and <i>B. rapa </i> (turnip), and detached leaves of <i>Erucastrum gallicum </i> (dog mustard). The biosynthetic relationship between indolyl glucosinolates and phytoalexins was investigated in rutabaga and turnip. The indolyl moiety of the phytoalexins cyclobrassinin (28), rutalexin (33), spirobrassinin (34), brassicanate A (43), and rapalexin A (53), as well as indolyl glucosinolates glucobrassicin (70), 4-methoxyglucobrassicin (156), and neoglucobrassicin (199) was confirmed to derive from L-tryptophan (78). The 1-methoxy-containing phytoalexins, erucalexin (38) and 1-methoxyspirobrassinin (35) were shown to derive from indolyl-3-acetaldoxime (112) through 1-methoxyindolyl-3-acetaldoxime (116). The 1-methoxy substituent of neoglucobrassicin was also shown to derive from 1-methoxyindolyl-3-acetaldoxime (116).<p>The incorporation of indolyl-3-acetothiohydroxamic acid (174) into the phytoalexins cyclobrassinin, rutalexin, brassicanate A, rapalexin A, and spirobrassinin, and into the glucosinolate glucobrassicin is reported for the first time. On the other hand, incorporation of 174 into 4-methoxyglucobrassicin and neoglucobrassicin was not detected under current experimental conditions. Cyclobrassinin was incorporated into spirobrassinin among the NH-containing phytoalexins, whereas sinalbin B (31) [biosynthesized from 1-methoxybrassinin (18)] was incorporated into erucalexin and 1-methoxyspirobrassinin. The efficient metabolism of [SC2H3]brassicanal A into [SC2H3]brassicanate A suggested a biogenetic relationship between these two phytoalexins, whereas absence of incorporation of indolyl-3-acetonitrile (49) into rutabaga phytoalexins or indolyl glucosinolates indicated that 49 is not a precursor of these secondary metabolites under the current experimental conditions.<p>The rutabaga and turnip tubers separately metabolized 1-methylindolyl-3-acetaldoxime (170) and 1-methylindolyl-3-acetothiohydroxamic acid (178) into 1-methylglucobrassicin (201); however, no 1-methyl-containing phytoalexins were detected in the extracts. Rutabaga tissues metabolized 1-(tert-butoxycarbonyl)indolyl-3-methylisothiocyanate (180) into 1-(tert-butoxycarbonyl)brassinin (181) and 1-(tert-butoxycarbonyl)spirobrassinin (196), whereas 1-acetylbrassinin (184) was the only detectable metabolic product of 1-acetylindolyl-3-methylisothiocyanate (183) in both rutabaga and turnip root tissues.<p>In conclusion, indolyl-3-acetothiohydroxamic acid (174) seems to be the branching point between brassinin and glucobrassicin. The biosynthetic pathway of NH-containing crucifer phytoalexins was mapped and follows the sequence L-tryptophan, indolyl-3-acetaldoxime, indolyl-3-acetothiohydroxamic acid, brassinin (possibly through indolyl-3-methylisothiocyanate), and other phytoalexins. The biosynthetic pathway of 1-methoxy-containing phytoalexins follows a similar sequence through 1-methoxyindolyl-3-acetaldoxime (biosynthesized from indolyl-3-acetaldoxime).

No description available.

This study is concerned with the development of simple and accurate alternative finite element models to displacement finite element models for geometrically nonlinear bending analysis of beams and plates. First, a unified corotational beam finite element that incorporates the kinematics of classical as well as refined beam theories, including the Timoshenko and Reddy beam theories, is developed in a single finite element. The governing equations are written in a "corotational" local frame that rotates with the element and with respect to which the standard linear engineering relations between strains and internal forces are valid. The element is based on Lagrange interpolation of the axial displacement, Hermite cubic interpolation of the transverse displacement, and related quadratic interpolation of the rotation, and it does not experience shear locking. The model is verified by comparisons with exact and/or approximate solutions available in the literature. Very good agreement is found in all cases. Next, a finite element model is developed using a mixed formulation of the first-order shear deformation theory of laminated composite plates. A p-type Lagrangian basis is used to approximate the nodal degrees of freedom that consist of three displacements, two rotations, and three moment resultants. The geometric nonlinearity, in the sense of the von Kµarman, is included in the plate theory. The mixed plate element developed herein is employed in the linear and nonlinear bending analysis of a variety of layered composite rectangular plates. The effects of transverse shear deformation, material anisotropy, and bending-stretching coupling on deflections and stresses are investigated. The predictive capability of the present model is demonstrated by comparison with analytical, experimental, and numerical solutions available in the literature. The model provides an accurate prediction of the global bending response of thin and moderately thick plates subjected to moderate and moderately large rotations. The inclusion of the bending moments at the nodes results in increased accuracy in the computation of stresses over those determined by conventional displacement-based finite element models. The many results presented here for geometrically nonlinear bending analysis of beams and plates should serve as reference for future investigations.

With the constantly evolving displayer technology, the liquid crystal displayer (LCD) has become widely utilized on the market. As a result, the demand for high-performance LCDs is on the rise. In addition to the color quality and contrast ratio, the brightness of a LCD is also an important issue in LCD applications. Since light source of the LCD depends on the backlight module, it is important to develop efficient a backlight module to improve the brightness of the LCD. The light guide plate (LGP), which makes use of our previously proposed step micro-structure, has two problems. The first is that the thickness limits the dimension of the LGP. The other is that the complex manufacturing process is not suitable for mass-production. Due to these difficulties, we proposed a new design containing periodic trapezoid micro-structures. The periodic micro-structures can be easily fabricated by the ejection-set process. In addition, the dimension of the LGP will not be limited by this new design. In this thesis, we will analyze the performance of our proposed structure and discuss the factors which might affect the output light intensity of the LGP. We made a few dozen prototyping LGPs and measured the output brightness of produced by these periodic micro-structures. The apparent transparent nature of our proposed LGPs is due to the fact that the dimension of the micro-structure is close to the wavelength. Thus the applications of the new LGPs are no longer limited to the LCD backlight modules. It can be also be used for example, as the reading light plate.