<p>A measurement of the production cross sections of top quark pairs in association with a W or Z boson is presented. The measurement uses 20.3 fb−1 of data from proton-proton collisions at √s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. Four different final states are considered: two opposite-sign leptons, two same-sign leptons, three leptons, and four leptons. The t t̅ W and t t̅ Z cross sections are simultaneously extracted using a maximum likelihood fit over all the final states. The t t̅ Z cross section is measured to be 176+58−52 fb, corresponding to a signal significance of 4.2σ. The t t̅ W cross section is measured to be 369+100−91 fb, corresponding to a signal significance of 5.0σ. The results are consistent with next-to-leading-order calculations for the tt̅W and tt̅Z processes.</p> / Dissertation

<p>A search for new heavy resonances decaying to boson pairs (WZ, WW or ZZ) using 20.3 inverse femtobarns of proton-proton collision data at a center of mass energy of 8 TeV is presented. The data were recorded by the ATLAS detector at the Large Hadron Collider (LHC) in 2012. The analysis combines several search channels with the leptonic, semi-leptonic and fully hadronic final states. The diboson invariant mass spectrum is studied for local excesses above the Standard Model background prediction, and no significant excess is observed for the combined analysis. 95$\%$ confidence limits are set on the cross section times branching ratios for three signal models: an extended gauge model with a heavy W boson, a bulk Randall-Sundrum model with a spin-2 graviton, and a simplified model with a heavy vector triplet. Among the individual search channels, the fully-hadronic channel is predominantly presented where boson tagging technique and jet substructure cuts are used. Local excesses are found in the dijet mass distribution around 2 TeV, leading to a global significance of 2.5 standard deviations. This deviation from the Standard Model prediction results in many theory explanations, and the possibilities could be further explored using the LHC Run 2 data.</p> / Dissertation

D techniques. A commercial off the shelf (COTS) imagery sensor able to distinguish near-infrared (NIR), near-ultraviolet (NUV), and visible wavelengths has been studied. The FOVEON image sensor, a multi-layer focal plane technology, was used in a simple camera implementation to test its viability as a multispectral imager. As expected the sensor functioned as both a visible and NIR detector. Vegetation was easily distinguished based on its NIR reflectance, and man-made materials could be effectively separated from the background.

In order for railgun technology to be relevant to the Infantry, the design of the projectile must incorporate the following three concepts: an effective ballistics package, geometries for aerodynamic stability; and a non-parasitic conducting armature. I designed an effective 30mm and scaled 40mm projectile which incorporates the aforementioned concepts. My ballistics analysis concluded with two AUTODYN. finite-element computer models that refined theoretical estimates for target penetration. The proposed railgun projectiles were effective in penetrating 100 mm of Rolled Homogenous Armor and in perforating 8 inches of Double Layered Reinforced Concrete. My theoretical analysis in aerodynamics predicts in-flight stability with a minimum static margin of approximately two percent. The analysis and modeling of the electromagnetic launch resulted in an adequate design. For this analysis, I used three Comsol Multiphysics. finite-element computer models. The modeling results validated fundamental railgun equations. The final projectile design concluded with a 3 m barrel and is characterized by the following parameters: conducting rails with an inductance gradient Å OÌ 0.38 Å IÌ H/m; an average temperature rise in the rails of 20 Å CÌ per shot; an effective current of less than 2 MA; and a projectile launch velocity of 1100 m/s.

The requirements of modern war have imposed the need for a low-cost, small-size, high-speed, large bandwidth, deployable Free-Space Optics (FSO) system that could be used to provide connectivity between major command centers and their subordinate units. Commercially available FSO systems are bulky and expensive. A preliminary low-cost FSO system was designed, based on commercial off the shelf (COTS) components, and tested over a 5ft. distance in a previous thesis done by Janaka P. Perera. The goal of this thesis is to improve the design and to extend the working range of the FSO. By improving beam collimation, adding precise mechanical movement and using assisting tools and techniques, the FSO network link was successfully established and tested over larger distances using 100Mbps. The maximum distance that could be achieved, with the on-hand optics and a 1mW transceiver, was 40m. Further calculations showed that the FSO link could be established over a 340m distance by using a 3mW transmitter and a 1-inch focuser in the receiver side.

A digital implementation of a phase sampling interferometer antenna system based on the Robust Symmetrical Number System (RSNS) is built using commercial-off-the-shelf (COTS) items. The RSNS-based direction finding (DF) system uses short baselines to achieve a high resolution DF capability in a physically compact system for use as stand-in sensors on unmanned aerial vehicles. The RSNS inherent integer Gray code property minimizes the possible encoding errors and adds a robustness to the accuracy of the estimated Angle of Arrival (AOA). A digital architecture using quadrature demodulators and real-time controllers provide grreater flexibility for signal processing and allows for the implementation of a new virtual spacing algorithm. The virtual spacing concept changes the RSNS moduli values to implement a virtual antenna spacing without having to physically change the antenna element spacing. This enables higher resolution DF in circumstances where the Signal-to-Noise Ratio is high enough to provide error free coding of the AOA. Two four element, digital 3-channel interferometer prototype systems were constructed and tested in the NPS anechoic chamber. The first antenna array is designed using pairwise relatively prime (PRP) moduli. When an extension of the virtual spacing concept for application to N-channel systems was successfully resolved, a second 3-channel array was built using non-PRP moduli for evaluating the performance of the virtual spacing concept. The simulated and experimental results, hardware implementation and testing procedures are presented in this thesis. Results for the first array show that the RSNS-based DF system is able to provide 0.7 degree RMS resolution with a baseline of 66 cm. For the second virtual spacing array, the short physical baseline of 14 cm was sensitive to noise and antenna spacing errors.

The employment of terahertz (THz) technology for applications including Improvised Explosive Device (IED) and concealed weapons detection is a rapidly growing field of research. Additionally, THz waves do not pose a health hazard as do x-rays and as such can be used for the imaging and detection of certain cancers. To date, however, most detectors are highly sophisticated, bulky systems which require extensive cooling in order to provide a signal-tonoise (SNR) ratio high enough for detection. A detection system that is simple in operation and uncooled is highly desirable and is the focus of this research. In this thesis, operation of a 3.4 THz quantum cascade laser (QCL) was successfully achieved using a closed cycle cryostat and nanosecond pulse generator with impedance matching circuitry. The laser beam was imaged in real time using an uncooled microbolometer infrared camera typically used in far-infrared wavelength band (8-12 mm). The preliminary findings offer potential for development of a compact THz imaging system for applications involving concealed object detection.

<p>Kravets, Vira V. (Ph.D., Physics) Optical properties of plasmonic nanostructures for bio-imaging and bio-sensing applications Dissertation directed by Associate Professor Anatoliy Pinchuk. ABSTRACT This dissertation explores the physics of free electron excitations in gold nanoparticle chains, silver nanoparticle colloids, and thin gold films. Electron excitations in nanostructures (surface plasmons, SP) are responsible for unique optical properties, which are applied in bio-sensing and bio-imaging applications. For gold nanoparticle chains, the effect of SP on resonance light absorption was studied experimentally and theoretically. Mainly, how the spectral position of the absorption peak depends on inter-particle distances. This dependence is used in ?molecular rulers?, providing spatial resolution below the Rayleigh limit. The underlying theory is based on particle interaction via scattered dipole fields. Often in literature only the near-field component of the scattered field is considered. Here, I show that middle and far fields should not be neglected for calculation of extinction by particle chains. In silver nanoparticles, SP excitations produce two independent effects: (a) the intrinsic fluorescence of the particles, and (b) the enhancement of a molecule?s fluorescence by a particle?s surface. The mechanism of (a) is deduced by studying how fluorescence depends on particle size. For (b), I show that fluorescence of a dye molecule on the surface of a nanoparticle is enhanced, when compared to that of the free-standing dye. I demonstrate that the dye?s fluorescent quantum yield is dependent on the particle?s size, making labeled silver nanoparticles attractive candidates as bio-imaging agents. Labeled nanoparticles are applied to cell imaging, and their bio-compatibility with two cell lines is evaluated here. Finally, in gold films under attenuated total internal reflection (ATR) conditions, the SP create a propagating wave (SP-polariton, SPP) when coupled with the incident light. Because of the sensitivity of SPPs to the medium adjacent to the gold film surface, they are widely applied in bio-sensing applications. A toolbox for the description of sputter-deposited gold films is presented here: it employs three experimental techniques (ATR, transmittance and atomic force microscopy) in combination with the effective medium theory for double-layered film model. Our findings have allowed for the avoidance of superficial fitting parameters in our model.

<p> A wealth of astrophysical research supports the existence of dark matter in the universe, yet the exact identity and nature of this unknown particle remain elusive. The Weakly Interacting Massive Particle (WIMP), one of the most promising dark matter candidates, is thought to interact with Standard Model particles only through the gravitational and weak nuclear forces. The Large Underground Xenon (LUX) experiment is one of a large number of experiments that seek to detect WIMPs through their rare but discernible scatters off of target nuclei. Specifically, LUX is a 370-kg dual-phase xenon-based time projection chamber (TPC) that operates by detecting light and ionization signals from particles incident upon a xenon target. The first part of this dissertation details the design of the LUX experiment and describes several novel hardware subsystems that allow LUX to detect extremely rare events with high precision. With the 2013 release of the world's first sub-zeptobarn spin-independent WIMP-nucleon cross section limit, the LUX (Large Underground Xenon) experiment has emerged as a frontrunner in the field of dark matter direct detection. </p><p> However, tension between experiments and the absence of a definitive positive detection suggest it would be prudent to search for answers outside the standard spin-independent/spin-dependent analyses. hi particular, the standard analyses neglect momentum- and velocity-dependent interactions on the grounds that WIMP-nucleus collisions are nonrelativistic. At the parton level, this is not always the case, and moreover, models exist in which the standard spin-independent and spin-dependent interactions are subdominant to new kinds of interactions. Recent theoretical work has identified a complete set of 14 possible independent WIMP-nucleon interactions using basic symmetries and an effective field theory formulation. These interactions produce not only spin-independent and spin-dependent nuclear responses but also novel nuclear responses such as angular-momentum-dependent and spin-orbit couplings. In the second portion of this dissertation we report on the extension of the LUX analysis to search for all 14 of these operators, we comment on the possible suppression of event rates due to operator interference, and we show that under this new framework, LUX again exhibits world-leading sensitivity.</p>

Clinical imaging and biopsies are major tools for cancer diagnosis. We explore whether serial imaging coupled with a mathematical model could test and refine patient specific forecasts for therapy outcomes.<p> We first examine whether parameters for a basic mathematical tumor model can be extracted from diffusion-weighted images (DW-MRI) and used for early detection of drug resistance to targeted therapy. We find that incorporating the spatial information available in clinical images improved the parameter extraction accuracy by an order of magnitude. Using statistical methods to compare the predictions of models with and without resistance, we find our method can identify tumor resistance well before current standards.<p> As the mixing of phenotypes within a tumor is not known, we proposed two possibilities for the spatial mixing of drug resistant and sensitive cell types, namely, a free diffusion and a constrained diffusion model. From experiments, we find that the resistant cell line spreads more rapidly than the sensitive cell line; that the diffusion constant describing the spread of resistant cells decreases with cell density; and that the sensitive cells reach higher packing density. Subsequent experiments find that asymptotic cell packing varies across tumor subtypes. As both candidate models assume constant diffusion rates and uniform packing, neither model agrees quantitatively with the mixing experiments. For the experimental parameter ranges, both models are equally effective at identifying resistance from serial DW-MRI.<p> We find that both protein expression, measurable from biopsies, and the microenvironment impact tumor resistance. For the non-small cell lung cancer line investigated, the concentration of the receptor c-Met increases the likelihood of positive growth under therapy (resistance). Here, we find that the growth rate varies with the logarithm of the microenvironment stiffness, indicating that not all tumors positive for pro-proliferation markers will be resistant. Taken together, our work presents a promising method to incorporate clinical imaging and tumor biopsies towards refining tumor models and forecasting patient specific treatment response.<p>