• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2803
  • 1421
  • 945
  • 220
  • 211
  • 142
  • 76
  • 58
  • 56
  • 55
  • 55
  • 55
  • 55
  • 55
  • 47
  • Tagged with
  • 7077
  • 1564
  • 574
  • 539
  • 445
  • 425
  • 380
  • 364
  • 347
  • 339
  • 314
  • 304
  • 261
  • 260
  • 244
  • 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.

Modeling High Altitude Electron Density Plumes Using Direct Numerical Simulation

Paro, Autumn D 15 April 2014 (has links)
Electron densities form field-aligned structured regions in the natural ionosphere and after a high altitude nuclear explosion (HANE). These electron densities, known as plumes, are made up of many smaller individual field-aligned regions called striations. Striation modeling for systems effects has traditionally been done use a statistical approach. This statistical approach evolves different moments of the electron density. Due to lack of test data it has never been validated. The purpose of this project was to use a direct numerical simulation to solve equations governing the differential motion of individual striations. It was done in five steps: 1) Transport a single striation, 2) solve potential equation, 3) combine transport and potential equations, 4) optimize combined solver, and 4) simulate a fully-striated plume for comparison with the statistical model.

Glow Discharge Characteristics of Non-thermal Microplasmas at above Atmospheric Pressures and their Applications in Microscale Plasma Transistors

Wakim, Dani Ghassan 16 December 2013 (has links)
A microscale plasma transistor capable of high speed switching was manufactured using microfabrication techniques and operated using microplasma discharges. Such a device has feature sizes on the order of 25 μm, is robust against spikes in power, high temperatures, as well as electromagnetic interference and capable of low cost production through microfabrication. In this work two aspects of the Microscale Plasma Device development were investigated; (1) the microplasma properties and (2) the manufacturing of the MPD. To study the required plasma discharges and develop them to become better suited for the task at hand, Direct Current (DC) plasma discharge characteristics were investigated under pressures from atmospheric to 1.65 MPa while varying current from 0.1 mA to 4.5 mA and gap length from 5 μm up to 250 μm. This testing was carried out in a high pressure test chamber fitted with a micrometer for variable electrode spacing and gas inlets and outlets for varying the working gas and pressure. Voltage and current measurements along with microscopic imaging and optical emission spectroscopy were taken for discharges in the varying gases to determine discharge V-I characteristics, sizes and temperatures. Data gathered was used to understand the microdischarge characteristics and tailor the plasma for application in the microtransistor. Discharges with diameters as small as 7 μm have been achieved in Nitrogen and 16.7 μm in Helium by operating at low current, 0.5mA, and at pressures of 1.65 MPa and 0.34 MPa respectively. Paschen type, Pd, scaling is observed both in breakdown voltages, steady state voltage, and discharge size from 0.1 MPa to 1.65 MPa. The discharges operated in a normal glow regime with near constant normalized current densities and relatively flat voltage current characteristics indicating normal glow discharge behavior in the microplasmas. During device development small diameter metal wires, 25 μm and 50 μm, were used to carry out experiments on the microscale device to aid in electrode and substrate material selection. Robust electrode and substrate materials were required to withstand high discharge temperatures in order to prolong the device life time. As material selection was narrowed down microfabrication techniques were utilized to achieve smaller electrode geometry and electrode gap spacing with greater consistency. Photolithography coupled with thin film deposition using metal evaporation and electroplating resulted in electrodes with features and electrode gap spacing on the order of 25 μm and film thicknesses of 35 μm. Aluminum, Nickel, Copper and Titanium were deposited onto Alumina (Al_(2)O_(3)) and Ceria Stabilized Zirconia (CSZ) ceramic substrates, where only the latter two electrode materials proved to be robust enough to withstand the discharge temperatures. Superficial oxide layers on the electrode surfaces provided a protective coating, prolonging electrode lifetime in atmospheric air from 360 seconds to greater than 400 seconds without metal evaporation occurring. The oxide coating also acted as a dielectric barrier and increasing the resistance of the electrode surfaces to the order of 300 MΩ in some cases thus acting as a ballast resistance, compensating for stray capacitance and helped stabilize the plasma discharge.

La tension superficielle du plasma et du sérum sanguins avec applications à l'étude de la coagulation du sang /

Cosmovici, N.L., January 1915 (has links)
Thèse de doctorat--Sciences naturelles--Faculté des sciences de l'Université de Paris, 1915. N°: 1569. / Notes bibliogr.

Molecular dynamics simulation of charged dusts in plasmas

Chen, Zhaoyang. January 2004 (has links) (PDF)
Bochum, Univ., Diss., 2004. / Computerdatei im Fernzugriff.

Analyse dynamischer Volumenprozesse in komplexen Plasmen

Goldbeck, Dirk David. January 2003 (has links)
München, Univ., Diss., 2003. / Dateien in unterschiedlichen Formaten. Computerdatei im Fernzugriff.

Gyrokinetische Simulation von Plasmaturbulenz mit gefangenen Teilchen und elektromagnetischen Effekten

Dannert, Tilman. January 2005 (has links) (PDF)
München, Techn. Universiẗat, Diss., 2005.

Rayleigh-Streuung und Strahlungsumverteilung an Helium in einer magnetischen Multipol-Plasmaquelle

Drepper, Petra. January 2000 (has links) (PDF)
Bochum, Universiẗat, Diss., 2001.

Analyse dynamischer Volumenprozesse in komplexen Plasmen

Goldbeck, Dirk David. January 2003 (has links)
München, Universiẗat, Diss., 2003. / Dateien in unterschiedlichen Formaten.

Plasmagleichgewichte in einer Kerr-Metrik

Kot, Yauhen. January 2003 (has links) (PDF)
Bochum, Universiẗat, Diss., 2003.

Molecular dynamics simulation of charged dusts in plasmas

Chen, Zhaoyang. January 2004 (has links) (PDF)
Bochum, University, Diss., 2004.

Page generated in 0.0631 seconds