• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 27
  • 6
  • 5
  • 4
  • 2
  • 1
  • 1
  • Tagged with
  • 52
  • 12
  • 9
  • 9
  • 7
  • 7
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Search for New Physics in the Exclusive $\gamma_{Delayed}$ + Missing Transverse Energy Channel in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV

Asaadi, Jonathan 14 March 2013 (has links)
This dissertation presents the results of a search in the exclusive photon plus missing transverse energy (gamma + E/_T) final state in proton antiproton collisions at center of mass energy of 1.96 TeV using the Collider Detector at Fermilab experiment. The strategy used here is to search for delayed photons coming from gauge mediated supersymmetric events with the exclusive production of ~X(0 1) -> gamma~G. In these models the ~X(0 1) is the lightest neutralino and has nanosecond lifetime before decaying to a photon (gamma) and gravitino (~G) which exits the detector unrecorded. In order to search for this process we select collisions that have a single photon plus missing transverse energy and little other activity in the detector and examine the arrival time of the photon. This arrival time is then compared against expectations from a data driven background of the standard model sources. In the data collected from the Fermilab Tevatron collider from December 2004 to June 2010, representing 6.3 fb^-1 of data, we observe 322 events in the photon arrival timing region from 2 nanoseconds to 7 nanoseconds with a data driven background prediction of 257 +/- 35. An excess of 65 events is observed, equivalent to a standard deviation (N_sigma) of 1.65 from the null hypothesis.
2

The Study of Material and Optical Properties for Cr-doped Fibers

Wang, Bo-Cyuan 23 July 2010 (has links)
With the rapid growth of optical telecommunication, the low-loss windows from 1.3 to 1.6 £gm are available by using the technology of dry fiber fabrication. The operation range such as commercial Er-doped fiber amplifiers (EDFAs) is only 70 nm, so it is interesting to develop the broadband fiber amplifiers. The Cr ions classified into transition metals are doped in specific host materials to be a gain medium. The spectra near infrared range have shown 300 nm. In this study, we measure and develop the material and optical properties of Cr-doped fibers (CDFs) fabricated by drawing-tower technology. In the fabrication of CDFs using rod-in-tube (RIT), the smallest loss at 1550 nm is 0.08 dB/cm. The composition of core is 84% SiO2 and the structure is almost amorphous, but there is a little £^-Al2O3 nano-crystalline structure. In the fabrication of CDFs using modified RIT (MRIT), the smallest loss is 0.03 dB/cm. Both of CDFs fabricated by RIT and MRIT, the fluorescence intensity is weak. In the fabrication of CDFs using powder-in-tube (PIT), the smallest loss is 0.33 dB/cm. The 3dB emission spectrum is from 0.8 to 1 £gm and power density is 6 nW/10nm. The profile of spectra is difference because of Cr ions in distorted structure which allowed a wide distribution of sites. In the future, measure absorption spectra and analyze the core¡¦s composition dependence of the emission of CDFs to provide fabrication optimization. Promoting the spontaneous emission intensity makes CDFs for novel fiber lasers and broadband fiber amplifiers.
3

Search for supersymmetry using rare B to mumu decays at CDF run II

Krutelyov, Vyacheslav 12 April 2006 (has links)
A search for rare B0 s -> µ+µ- and B0d -> µ+µ- decays has been performed in pp collisions at sqroot(s) = 1.96 TeV using 364 pb-1 of data collected by the CDF II experiment at the Fermilab Tevatron Collider. The rate of each decay is sensitive to contributions from physics beyond the Standard Model (SM). No events pass the optimized selection requirements, consistent with the SM expectation. The resulting upper limits on the branching ratios are B(B0s -> µ+µ-) < 1.5 x 10-7 and B(B0d -> µ+µ-) < 3.8 x 10-8 at the 90% confidence level. The limits are used to exclude some parameter space for several supersymmetric models.
4

Heavy flavor decay of Zgamma at CDF

Harrington-Taber, Timothy M. 01 December 2013 (has links)
According to the Standard Model of particle physics, elementary particles interact via the exchange of mediator particles. The specific mediator particle depends on the force: gluons for the strong nuclear force, photons for the electromagnetic force, and W and Z bosons for the weak nuclear force. No quantum theory of gravity has been deemed adequate by the community at this time, and no gravity-mediating particle (graviton is the proposed name for such a particle) is included in the Standard Model. As gravity is much weaker than the other fundamental forces at the particle level, this does not currently pose practical difficulties for elementary particle physics. In order to specifically study W and Z bosons, it is necessary to generate high-energy beams of particles, which are collided, and whose collisions (hopefully) produce the 90 GeV required for Z boson production. Typically, electrons and protons are the particle of choice for these beams. In order to obtain the necessary energies, circular collider facilities have been the highest energy sites for years. As electrons radiate energy when in circular orbits, by the late 1980's proton colliders have been the primary choice for high-energy physics. One such collider, built at Fermilab National Accelerator Laboratory in Batavia, Illinois, was the Tevatron, which started operations in 1984 and finally shut down in 2011. The Tevatron collided protons with anti-protons with a center of mass energy of 1.96 TeV for ten years (2001-2011) after a series of upgrades known collectively as Run II. Of the two detectors at the Tevatron, this analysis considers events observed at the Collider Detector at Fermilab (CDF) during Run II. Results can be usefully cross-checked by the other detector, D0. This thesis includes a technical description of the silicon tracking system at the CDF detector, including an account of challenges encountered during its operation and some of the personal work done to assist in its continuing operation. This analysis measures the frequency at which two bosons are created (specifically, a photon and a Z boson) in a particular decay channel (namely, the Z decays into two b quarks). This diboson production is frequently measured, but typically only in leptonic decays at hadron colliders, as there is less background in these channels. This analysis attempts to provide a useful confirmation on these experiments by analyzing the diboson production in an independent decay channel. As the event signature is also produced by strong force interactions, this electroweak signal composes a relatively small fraction of the events observed at CDF. In order to distinguish between the two, an artificial neural network was trained to separate the signal events from the primary background. While the result was measured to be consistent with the Standard Model prediction, large statistical and significant systematic errors limit the utility of this measurement.
5

Fabrication of Cr-Doped Fiber by Drawing Tower

Huang, Yu-ming 15 July 2006 (has links)
Abstract The breakthrough technology in dry fiber fabrication has opened the possibility for using fiber bandwidths all the way from 1.3 to 1.6 £gm. The fiber amplifier that is in common use can not fully cover the whole, which its range is from 1.3 to 1.6 £gm. Recently, the Cr4+-doped fiber has shown a broadband emission from 1.3 to 1.6 £gm. Therefore, it is eminently suitable for super-wideband optical source. In this study, we first propose and fabricate a Cr4+-doped fiber by employing a commercial drawing-tower method, which has good core diameter uniformity, the growth speed is up to 200 m/min, and the core diameter is less than 10 £gm. The central wavelength of the ASE spectrum is at 1310 nm, and a 3-dB bandwidth is 300 nm. The divergent angle of the Cr-doped fiber is 17 o ¡Ñ 15 o and it¡¦s also similar to a single mode fiber of 16 o ¡Ñ 16 o. Low-loss fusion splice can readily be done with the standard single mode fiber, and is beneficial when integrated with the broadband WDM couplers. Therefore, it is good for commercial production and application to light wave systems.
6

Search for the Higgs Boson in the ZH → μ<sup>+</sup>μ<sup>−</sup>bb̄ Channel at CDF Using Novel Multivariate Techniques

Pilot, Justin Robert 15 December 2011 (has links)
No description available.
7

Mission Analysis and Reporting System (MARS) - EW Analysis and Reporting On A Personal Computer

Burton, Ken 10 1900 (has links)
International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / In response to the need to analyze and report upon Electronic Warfare (EW) test data results in a comprehensive and uniform manner, the Mission Analysis and Reporting System (MARS) has been developed. MARS is a government owned PC based Windows application designed for rapid analysis and reporting upon EW test mission data. MARS currently performs Jammer Effectiveness ( Reduction In Lethality, Increase In Survivability, Reduction In Shot, and Reduction In Hit), Radar Warning Receiver (RWR) System performance (Threat ID, Response Time/Ageout, and Direction Finding (DF) Accuracy), and Tracking Error Statistics. Additionally, MARS produces several graphical outputs including polar plotting, dynamic strip charting, Cumulative Distribution Functions (CDF), and RWR Simulated Scope. Continual development and maintenance of MARS at the Air Force Development Test Center, Eglin Air Force Base, Florida, has provided a proven product used by numerous DT&E and OT&E test projects over the last four years.
8

Functional Analysis of the Cation Diffusion Facilitator ZitB from Escherichia coli

Haney, Christopher J January 2007 (has links)
This research sought to elucidate the molecular mechanism by which a recently described family of ion transport proteins, the cation diffusion facilitators (CDFs), transfer ions across biomembranes. Using the Escherichia coli homologs ZitB, and FieF, as well as CzcD from Cupriavidus metallidurans CH34 as models, the amino acids essential to CDF function were identified, and the transport behavior of ZitB and its homolog FieF, were described.Site-directed ZitB mutants were used to determine the necessity of individual amino acids. The mutation of several well-conserved acidic residues resulted in the loss of a ZitB-mediated zinc-resistant phenotype in the zinc-sensitive E. coli strain GG48. ZitB also complemented the potassium uptake deficient strain TK2420, suggesting that ZitB works as an antiporter, possibly allowing potassium into the cell while effluxing zinc.This result was further investigated in experiments using everted membrane vesicles(EMVs). Vesicles bearing ZitB accumulated 65Zn(II) in a NADH-dependent manner, with an apparent KM of 1 micromolar. This accumulation was inhibitable by the protonophore FCCP, suggesting CDF dependence upon the proton motive force. Similar results were obtained using both EMVs and proteoliposomes containing the CDF homologs CzcD, from C. metallidurans CH34, and FieF from E. coli. Despite facilitating 65Zn(II) uptakeinto EMVs, fieF transcription was zinc and iron-dependent, but independent of the ironuptake regulator Fur. FieF expression in trans complemented the iron-sensitive phenotypeof a strain lacking fur, causing it to accumulate less 55Fe than wild type. Reconstituted proteoliposomes containing FieF also accumulated less 55Fe than those without.This research confirms that CDF proteins likely depend on the cell's proton gradient, effluxing substrate in a metal:proton antiport arrangement. Substrate acquisition and throughput is facilitated by a set of acidic amino acids and histidines. The relatively lowapparent KM of ZitB suggests a homeostatic role for the protein; however, the iron-inducibilityof fieF hints at a role in iron detoxification, so the cellular functions of the CDF family may be quite diverse, even within the bacteria.
9

Etude de la variabilité naturelle dans la réponse du peuplier aux métaux : Bases physiologiques et exploitation en phytoremédiation / Study of the natural variability in the response of poplar to heavy metals : physiological bases and potential in phytoremediation

Migeon, Aude 06 July 2009 (has links)
Les différentes études entreprises ont porté sur la détermination du potentiel accumulateur du peuplier à une fin d’utilisation en phytoremédiation. Chez les végétaux, les éléments traces comme le Zn, Fe, Cu, Co, Mn, Mo et Ni sont nécessaires aux processus biologiques mais leur accumulation excessive peut être toxique. D’autres éléments non essentiels comme le Cd et le Pb peuvent également être absorbés par les végétaux, et donc constituer un danger potentiel puisqu’ils entrent ainsi dans la chaîne alimentaire. La phytoremédiation est l’utilisation de plantes et de leurs microbes associés pour la dépollution de l’environnement. Dans le cadre de cette étude, il a été démontré que le peuplier (Populus spp.) pouvait accumuler de relativement fortes concentrations de certains métaux (Cd, Zn et Ni) par rapport à d’autres espèces ligneuses, par exemple 30-50 µg de Cd /g de matière sèche foliaire, soit 20 fois plus que les autres espèces. Après avoir mis en évidence le potentiel accumulateur du peuplier, nous avons testé différents cultivars en culture hydroponique et avons ainsi mis en évidence des potentiels accumulateurs variés entre cultivars. Nous avons montré que les hybrides de P. trichocarpa accumulaient davantage que les autres hybrides. Parallèlement à cette étude, nous avons implanté ces mêmes cultivars sur deux sites pollués dans le cadre du projet ANR PHYTOPOP. Combiné à la production d’une forte biomasse qui peut être utilisée pour produire de l’énergie, ce caractère accumulateur fait du peuplier un bon candidat pour la phytoremédiation. Les membres de la famille des CDF (Cation Diffusion Facilitator) sont impliqués dans le transport des métaux. Après une étude phylogénétique des membres de cette famille (démonstration d’un nombre supérieur de CDF chez le peuplier par rapport aux autres espèces), leur expression dans différents tissus et dans différentes conditions physiologiques (sur sol témoin et sur sol pollué) a été étudiée. De plus, la caractérisation fonctionnelle a permis de mettre en évidence un transporteur de Zn (PtMTP2) et un transporteur de Mn (PtMTP9). Une tentative de localisation de ces transporteurs a également été entreprise. Dans le but de localiser les métaux dans les tissus de la plante, nous avons effectué des analyses en spectrométrie de masse à ionisation secondaire (SIMS) sur des feuilles de peupliers soumis à un stress métallique. Cette dernière technique a permis de montrer que le Zn était essentiellement concentré au niveau du mésophylle. / The present study beared on the capacity of poplar to be used in phytoremediation programmes. In plants, trace elements such as Zn, Fe, Cu, Co, Mn, Mo and Ni are necessary to biological processes but they also can be toxic when present at high concentrations. Other non essential elements, such as Cd and Pb also can be taken up by plants and therefore constitute a potential risk for health via accumulation into the food chain. Phytoremediation is the use of plants and associated microorganisms to clean up the environment. First, we have shown that poplar (Populus) species could relatively accumulate high concentrations of metals (Cd, Zn and Ni) compared to other woody plants. For instance, poplar is able to accumulate 30 times more Cd than other woody species. Second we have measured in hydroponic cultures, the potential of metal accumulation by different poplar cultivars. We found that P. trichocarpa hybrids accumulated more metals than the other hybrids. As part of the PHYTOPOP programme, we have also grown the same cultivars on two different polluted sites. Finally, by secondary ion mass spectrometry, we were able to localize Zn in poplar leaf mesophyll. The high biomass, which can also be used for energetic processes, and the heavy metals accumulation properties of poplar lead to the conclusion that poplar can constitute a good candidate for phytoremediation. The CDF (Cation Diffusion Facilitator) members are proteins involved in the transport of heavy metals. Phylogenetic analyses of the CDF family have shown that poplar contains a higher number of CDF members compared with other species. Expression levels of CDF members were studied in different tissues and in different physiological conditions. Moreover, heterologous expression in yeast has shown that PtMTP2 and PtMTP9 transport Zn and Mn respectively. Localization experiments in planta were also realized.
10

Search for New Physics in the Exclusive Gamma+MET Final State in p-pbar Collisions at Sqrt(s) = 1.96 TeV

Aurisano, Adam 1982- 14 March 2013 (has links)
This dissertation presents a search for heavy, long-lived, neutral particles that decay to photons in proton anti-proton collisions with a center of mass energy of 1.96 TeV at the Collider Detector at Fermilab (CDF) experiment. Such particles are typical of models of Gauge Mediated Supersymmetry Breaking (GMSB). We select events with a single photon, missing transverse energy, and little other activity in the detector. We model the photon arrival time for Standard Model and non-collision sources using a data-driven method and consider photons which have a time of arrival at the detector which is significantly delayed relative to predictions. Using 6.3 fb^−1 of data collected from December 2004 to June 2010, we observe 322 events in the signal region compared to a background prediction of 287 ± 24 events. While the data are consistently above predictions, we report a model excess with a significance of 1.2 standard deviations from the null hypothesis.

Page generated in 0.0359 seconds