The sporadic accretion following the tidal disruption of a star by a super-massive black hole (TDE) leads to a bright. UV and soft X-ray flare in the galactic nucleus. The gas and dust surrounding the black hole responses to such a flare with an echo in emission lines and infrared emission. In this paper, we report the detection of long fading mid-IR emission lasting up to 14 years after the flare in four TDE candidates with transient coronal lines using the WISE public data release. We estimate that the reprocessed mid-IR luminosities are in the range between 4 x 10(42) and 2 x 10(43) erg s(-1) and dust temperature in the range of 570-800 K when WISE first detected these sources three to five years after the flare. Both luminosity and dust temperature decrease with time. We interpret the mid-IR emission as the infrared echo of the tidal disruption flare. We estimate the UV luminosity at the peak flare to be 1 to 30 times 10(44) erg s(-1) and that for. warm dust masses to be. in the range of 0.05-1.3 M-circle dot within a few parsecs. Our results suggest that the. mid-infrared echo is a general signature of TDE in the gas-rich environment.

Doctor of Philosophy / Department of Chemistry / Ryszard J. Jankowiak / This dissertation reports the low temperature frequency domain spectroscopic study of three different natural pigment protein complexes and one artificial antenna system. The main focus of this work is to better understand electronic structure, excitation energy transfer (EET), and electron transfer (ET) dynamics in these systems that could have impact on achieving higher efficiency in future artificial solar cells. In the first part of this dissertation, electronic structure and EET pathways in isolated intact CP43 prime protein complex, which is isolated from Cyanobacterium synechocystis PCC 6803 grown under iron stressed conditions, are investigated using low-temperature absorption, fluorescence, fluorescence excitation, and hole-burning (HB) spectroscopies. This work suggests that, in analogy to the CP43 complex of PSII core, CP43 prime possesses two quasi-degenerate low energy states, A prime and B prime. The various low-temperature optical spectra are fitted considering an uncorrelated EET model. This work suggests that for optimal energy transfer from CP43 prime to PSI, the A prime and B prime state chlorophylls belonging to each CP43 prime should face towards the PSI core. The second part of dissertation reports the photochemical HB study on novel Zinc bacterial reaction center (Zn-RC) from Rhodobacter sphaeroides and its β-mutant (Zn-β-RC). This study shows that ET in the two samples is similar; however, the quantum efficiency of charge separation in the mutant decreases by 60 %. This finding suggests that the coordination state of the HA site zinc bacteriochlorophyll does not tune the active branch ET. Simultaneous fits of various optical spectra using experimentally determined inhomogeneity provides more reliable electron phonon coupling parameters for the P870 state of both RC samples. In the last part of this dissertation, EET in a novel artificial antenna system (ethynyl linked chlorophyll trefoil, ChlT1) is investigated. EET time in ChlT1 is ~2 ps. ChlT1 in MTHF/ethanol glass forms four different types of aggregates, A1-A4. The EET time in A1 and A2 type aggregates slows down only by a factor of 5 and 7, respectively. This study suggests that ChlT1 and its aggregates can be used as efficient antenna systems in designing organic solar cells.

We identify three structures that lie in the parameter plane of the rational map F(z) = zⁿ + λ / zᵈ, for which z is a complex number, λ a complex parameter, n ≥ 4 is even, and d ≥ 3 is odd. There exists a Sierpindelbrot arc, an infinite sequence of pairs of Mandelbrot sets and Sierpinski holes, that limits to the parameter at the end of the arc. There exists as well a qualitatively different Sierpindelbrot arc, an infinite sequence of pairs of Mandelbrot sets and Sierpinski holes, that limits to the parameter at the center of the arc. Furthermore, there exist infinitely many arcs of each type. A parameter can travel along a continuous path from the Cantor set locus, along infinitely many arcs of the first type in a successively smaller region of the parameter plane, while passing through an arc of the second type, to the parameter at the center of the latter arc. This infinite sequence of Sierpindelbrot arcs is a Sierpinski Mandelbrot spiral.

In this thesis we exploit the setup of AdS3/CFT2 holography, and in particular the D1D5 two-dimensional CFT, to describe states dual to geometries relevant for the \fuzzball" proposal for the description of six-dimensional black hole microstates. Precise holographic dualities between CFT and bulk geometric objects are established and checked, both for 2 and 3-charge states. In particular, VEVs of CFT operators of small conformal dimension are checked to encode deviations from AdS3 geometry near the spacetime boundary. 4-point functions of the \heavy-heavy-light-light" type are also considered and matching is found between CFT and bulk computations via the usual AdS/CFT prescription, with the heavy states being dual to (simple) microstate geometries. In this context, the issue of the presence of spurious singularities at leading order in the large N limit is assessed and cancellations are found even without considering sub-leading corrections, at the cost of considering the full detail of the D1D5 CFT (i.e. including the Virasoro blocks of operators of small dimension charged under the internal SU(2)L SU(2)R R-symmetry group). Finally, more complicated 4-point functions, involving operators in the twisted sector of the CFT, are computed and the results are checked against known results in the literature with the aim of verifying the robustness of the (new) techniques used. Supersymmetric Ward identities are also derived, and checked for some cases, between correlators written in terms of bosons and in terms of fermions.

Biaxial tensile strained Si grown on SiGe virtual substrates will be incorporated into future generations of CMOS technology due to the lack of performance increase with scaling. Compressively strained Ge-rich alloys with high hole mobilities can also be grown on relaxed SiGe. We review progress in strained Si and dual channel heterostructures, and also introduce high hole mobility digital alloy heterostructures. By optimizing growth conditions and understanding the physics of hole and electron transport in these devices, we have fabricated nearly symmetric mobility p- and n-MOSFETs on a common Si₀.₅Ge₀.₅ virtual substrate. / Singapore-MIT Alliance (SMA)

In this thesis, we have analyzed one-dimensional fermion-spin interactions in the dilute limit. The two cases we analyze represent different paradigms. For the first part, we look at the existence of spins for all sites as an effective model to describe the rearrangement of core electrons within the dynamic Hubbard model. Within this model, the behavior of electrons and holes will be compared in the presence of fermion-spin coupling and on-site repulsion. It will be shown that in this framework, electrons and holes behave differently and even though electrons experience increased repulsion, holes show attraction for a range of on-site repulsions. The characteristics of the interaction show effective nearest-neighbor attraction though no such term exists within the model. By the analysis of dynamic properties, two regions of interaction are identified. The gradual change from weak to strong coupling of fermions is presented. The effect of introducing on-site repulsion for both ranges of coupling is presented for both the dynamic Hubbard model and electron-hole symmetric version. For the second case involving fermion-spin interaction, we look at the interaction of a fermion with spins existing only for a small portion of the lattice, representing a coupled magnetic layer that an itinerant fermion interacts with through Heisenberg-like spin flip interaction. The interaction represents a spin-flip interaction of a spin current and magnetic layer. This interaction has been extensively studied for its relevance to computer hard drives both experimentally and theoretically. Most theoretical descriptions utilize the semi-classical Landau-Lifshitz-Gilbert (LLG) formalism. However, with recent improvements in experimental methods with very small magnetic layers and very fast real time measurements, quantum effects become more pronounced. We present quantum mechanical results that show considerable modification to spin-flip interaction. We identify a set of conditions that exhibits the existence of an emerging bound state for the spin current both numerically and analytically. The bound state is a quantum mechanical state and cannot be achieved with a classical picture. We present results in a one-dimensional lattice for a spin-1/2 system, and generalize our arguments to higher dimension and spins with S > 1/2.

No description available.

The main objective of this study is to investigate the applicability of a new multilateral well architecture in the domain of small size and offshore gas fields. The new architecture completely reverses the current multilateral technology. The innovative concept suggests that laterals can be achieved like any conventional wells. They could be drilled from the surface and tied back to a common wellbore referred to as the mother well. Production would go through the toe of laterals into the mother well. The mother well could be as simple as a large diameter casing equipped with prepared connections to tie in feeder wells. This study looked past the mechanical challenge of achieving the new architecture. I demonstrated important benefits in terms of cost reduction, well completion and operations, and reservoir drainage. I looked at a typical field case, Phoenix, located in West Africa. Its actual development plan targets an ultimate recovery of 600 BCF with a total of four sub-vertical wells. I implemented a new development scenario with the innovative multilateral architecture. For comparison purposes, I achieved a reservoir simulation and a production forecast with both scenarios. The only simulation variable was the well architecture definition. As a main result, the new multilateral structure could produce as many as four vertical wells with three slim-hole laterals. I achieved a quantitative risk analysis on both development plans. I assessed the development cost of each scenario and performed a Monte Carlo simulation to account for cost uncertainties. In addition to the actual 70 MMSCFD gas contract, I simulated a progressive gas demand increase of 20 MMSCFD every five years and a 150 MMSCFD gas market. The study demonstrates the economic benefits of the new technology in the domain of offshore and small gas fields. This work also shows that this new generation of multilaterals brings new option values to the domain of multilateral technology.

Organic Light Emitting Diodes (OLEDs) are widely viewed as next generation platform for flat panel displays and solid state lighting. Currently, OLED efficiency is not high due to high driving voltage. Molybdenum trioxide (MoO3) is ideal for p-type doping of the wide bandgap organic semiconductor 4,4’-bis-9-carbozyl biphenyl (CBP). With p-type doped CBP layer as Hole Transport Layer (HTL), driving voltage can be significantly reduced. Effective design for doped OLED structure consists of a HTL with doped layer from 20nm to 40nm and MoO3 concentration above 5%, the optimized OLED with doped CBP HTL present an 18% improvement over a standard device with CBP HTL at 100mA/cm2. Injection is found to be the principle cause of the reduction of driving voltage and shows close relations to doped layer thickness. Also charge balance is an important factor for high current efficiency, doped layer can be used as tools to promote charge balance.

Organic Light Emitting Diodes (OLEDs) are widely viewed as next generation platform for flat panel displays and solid state lighting. Currently, OLED efficiency is not high due to high driving voltage. Molybdenum trioxide (MoO3) is ideal for p-type doping of the wide bandgap organic semiconductor 4,4’-bis-9-carbozyl biphenyl (CBP). With p-type doped CBP layer as Hole Transport Layer (HTL), driving voltage can be significantly reduced. Effective design for doped OLED structure consists of a HTL with doped layer from 20nm to 40nm and MoO3 concentration above 5%, the optimized OLED with doped CBP HTL present an 18% improvement over a standard device with CBP HTL at 100mA/cm2. Injection is found to be the principle cause of the reduction of driving voltage and shows close relations to doped layer thickness. Also charge balance is an important factor for high current efficiency, doped layer can be used as tools to promote charge balance.