671 |
Social Movement & Social Media : A qualitative study of Occupy Wall StreetClark, Eric January 2012 (has links)
This project is important to the research in both the fields of social movement and of social media and their growing relationship. This report has analyzed the responses of several key role players in one of the biggest social movements in American history, Occupy Wall Street. Social media was used as a tool for both communication and information gathering amongst all those who were involved in the movement in a variety of capacities. The relationship and change that is occurring between traditional media and social media as information sources is also examined. Through qualitative analysis the importance that the role that social media now commands in our society in the context of social movements specifically became clear. The results will show the significance of this work and its importance in understanding the role that social media will continue to play in future social movements in the digitized public sphere of the 21st century. / Article manuscript 7,5 hp par of degree:<em> ‘Social media is our media’: two individual activists’ perspectives oftheir relationship with the uses of traditional and social media duringOccupy Wall Street</em>
|
672 |
Single Wall Carbon Nanotube/Polyacrylonitrile Composite FiberLiang, Jianghong 01 November 2004 (has links)
Single Wall Carbon Nanotubes (SWNTs), discovered in 1993, have good mechanical, electrical and thermal properties. Polyacrylonitrile (PAN) is an important fiber for textiles as well as a precursor for carbon fibers. PAN has been produced since 1930s.
In this study, we have processed SWNT/PAN fibers by dry-jet wet spinning. Purified SWNT, nitric acid treated SWNTs, and benzonitrile functionalized SWNTs have been used. Fiber processing was done in Dimethyl Formamide (DMF) and coagulation was done in DMF/water mixture. The coagulated fibers were drawn (draw ratio of 6) at 95 oC.
Structure, orientation, and mechanical properties of these fibers have been studied. The cross-sections for all the fibers are not circular. Incorporation of SWNT in PAN results in improved mechanical properties, tensile modulus increased from 7.9 GPa for control PAN to 13.7 GPa for SWNT/PAN composite fiber, and functionalized SWNTs result in higher improvements with tensile modulus reaching 17.8 GPa for acid treated SWNT/PAN composite fibers. The theoretical analysis suggests that observed moduli of the composite fibers are consistent with the predicted values.
|
673 |
The art of building (Baukunst) of Mies van der RoheKim, Ransoo 12 May 2006 (has links)
This dissertation attempts to interpret the statements of Ludwig Mies vans der Rohe (1886-1969) that pertain to his lifelong theory of Baukunst, or the art of building in terms of tectonics. In order to use the concept tectonics as a criterion according to which one can comprehend Mies words and works, this dissertation attempted to define tectonics in a more general sense by collecting existing definitions and categorizing them. The result of this endeavor showed that tectonics does not signify a supportive structure but the art of framing construction, in which linear elements are put together with joints and clad or infilled with lightweight material. It is proposed that Mies, who called the ideal of tectonic architecture the art of building, during his lifelong career, experienced two periods of critical awareness through which he established his own type of tectonic buildings: awareness of the open plan and then that of clear space. After the former occurred in 1926, he focused on the creation of inner spatial openness; after the latter, which this dissertation proposes occurred around 1930, when he met Karlfried Graf Drckheim (1896-1988), who had been absorbed in Lao-tzus philosophy, Mies intended to show that his architectural concern was beyond physical construction by employing the concept of changing nature and by designing his buildings to be neutral frames. Mies finally achieved a tectonically integrated body of a building that contained extroverted and undetermined space, which he referred to as clear space, or generally called Mies universal space, through his lifelong pursuit for the accomplishment of his own art of building, which this dissertation terms Miesian tectonics.
|
674 |
Spin-transfer Torque in Magnetic NanostructuresXiao, Jiang 30 May 2006 (has links)
This thesis consists of three distinct components: (1) a test of Slocnzewski's theory of spin-transfer torque using the Boltzmann equation, (2) a comparison of macrospin models of spin-transfer dynamics in spin valves with experimental data, and (3) a study of spin-transfer torque in continuously variable
magnetization.
Slonczewski developed a simple circuit theory for spin-transfer torque in spin valves with thin spacer layer. We developed a numerical method to calculate the spin-transfer torque in a spin valve using Boltzmann equation. In almost all realistic cases, the circuit theory predictions agree well with the Boltzmann equation results.
To gain a better understanding of experimental results for spin valve systems, current-induced magnetization dynamics for a spin valve are studied using a single-domain approximation and a generalized Landau-Lifshitz-Gilbert equation. Many features of the experiment were reproduced by the simulations. However, there are two significant discrepancies: the current dependence of the magnetization precession frequency, and the presence and/or absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature.
Spin-transfer effects in systems with continuously varying magnetization also have attracted much attention. One key question is under what condition is the spin current adiabatic, i.e., aligned to the local magnetization. Both quantum and semi-classical calculations of the spin current and spin-transfer torque are done in a free-electron Stoner model. The calculation shows that, in the adiabatic limit, the spin current aligns to the local magnetization while the spin density does not. The reason is found in an effective field produced by the gradient of the magnetization in the wall. Non-adiabatic effects arise for short domain walls, but their magnitude decreases exponentially as the wall width increases.
|
675 |
Electroluminescence of Layer Thickness, Carbon Nano-particle Dopants, and Percolation Threshold Electric Conductivity of Fully Conjugated Rigid-rod PolymerChang, Chih-hao 02 July 2010 (has links)
Polymer light emitting diodes (PLED) were using a heterocyclic aromatic rigid-rod polymer poly-p-phenylene-benzobisoxazole (PBO) as an opto-electronically active layer; and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) as a hole transporting layer. Aluminum (Al) and indium tin oxide (ITO) were served as device cathode and anode, respectively. [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) or derivatized multi-wall carbon nano-tube (MWCNT-C18), with great electron transporting ability, was doped into PBO to enhance the performance of PLED devices as well as the thin-film electrical conductivity.
The optical length was changed by using different spin coating speeds and durations. From the research, the £fmax of electroluminescence (EL) was blue-shifted as PEDOT:PSS spin coating speed increased for a thinner layer. Once using a higher spin coating speed repeatedly to coat PEDOT:PSS, the £fmax of electroluminescence was red-shifted. If the PEDOT:PSS film thicknesses were similar, the EL spectra were almost the same, independent of device processing scheme.
The injection current and EL intensity were enhanced by doping PC61BM or MWCNT- C18. The electric conductivity parallel to film surface (£m¡ü) was increased as the doping concentration increased. Because of the extremely different aspect ratio, the MWCNT-C18 had a lower percolation threshold concentration. Therefore, at a low MWCNT-C18 doping concentration, the injection current and the EL intensity were enhanced compared with those of PC61BM.
|
676 |
The Study of Concentration Effect of Carbon Nanotube Based Saturable Absorber on Mode-Locked PulseChen, Xi-zong 20 July 2010 (has links)
We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the Erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was 1 to 4.5% as the thickness increased from 18 to 265 £gm. We obtained the stable pulse of the mode-locked EDFL (MLEDFL) when the full-width half-maximum (FWHM) decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased from 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps was the thickness of SWCNTs SA increased from 8 to 100 £gm.
In EDFL system, we vary group-velocity dispersion (GVD) with different cavity length to achieve optical pulse compression. We got the shortest pulsewidth was 713 fs, and the time-bandwidth product (TBP) was 0.345. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.
|
677 |
Study on Nonlinear Self-Phase Modulation Enhancement in Passive Mode Locked Fiber Laser with Single-Wall Carbon Nanotube Saturable AbsorberChiu, Jin-Chen 20 December 2010 (has links)
The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulse width in passively mode-locked erbium-doped fiber ring laser (MLEDFL) was investigated and measured. The TCP represented the amounts of SWCNTs, which the optical beam encountered when passing through the SWCNTs SA. If the TCP was smaller than 8.25 (£gm x wt%), the spectral bandwidth was below 2 nm. The pulse shaping was dominated by its own self amplitude modulation (SAM) of SWCNTs SA. With further increasing TCP, the soliton-like ML operation was achieved and the spectral bandwidth was expanded to 6 nm. For soliton-like mode locking (ML) operation, the area theorem dominated the pulse shaping.
Through area theorem analysis, the estimation of SPM increased as the TCP increased. The adequate enhanced SPM for balancing the slight negative GVD was provided to generate soliton-like ML pulses shorten the pulse width. However, as the TCP increased, the soliton pulse energy decreased. The decreasing soliton pulse energy restricted the further pulse shortening. The results showed that the dependence of the pulse energy and nonlinear self phase modulation (SPM) on TCP enabled to determine the shortest pulse width in MLEDFL based on the area theorem. At optimized TCP of 70.93 (£gm x wt%), it was found that the shortest pulse width of 418 fs.
In addition, based on the estimated SPM from area theorem, the nonlinear refractive index n2 was calculated at the level of 0.4 - 1 x 10^-15 m^2/W that was close to the literature values of 10^-15 - 10^-16 m2/W. It provides another way to estimate the nonlinear refractive index except for the Z-scan measurement. We could also estimate the SPM if an active Z-scan measurement was taken to obtain the nonlinear refractive index of the sample. We realized the trend of pulse energy through few samples in MLEDFL, the behavior of pulse width could be theoretically simulated based on area theorem. Hence, with the area theorem analysis, the optimized TCP of SWCNTs SA could be simulated and estimated to generate the shortest pulse width from the trends of pulse energy and estimated SPM. The significant effect of TCP on pulse energy, SPM, pulse width, and spectral bandwidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of key parameters for characterizing the passive MLFL pulse width. Through the study of the dependence of TCP on ML pulses in MLEDFL, it may provide a guideline to fabricate an effective SWCNTs SA to generate the shortest pulse width of the MLEDFL.
|
678 |
Computational fluid dynamics (CFD) simulations of aerosol in a u-shaped steam generator tubeLongmire, Pamela 15 May 2009 (has links)
To quantify primary side aerosol retention, an Eulerian/Lagrangian approach was
used to investigate aerosol transport in a compressible, turbulent, adiabatic, internal,
wall-bounded flow. The ARTIST experimental project (Phase I) served as the physical
model replicated for numerical simulation. Realizable k-ε and standard k-ω turbulence
models were selected from the computational fluid dynamics (CFD) code, FLUENT, to
provide the Eulerian description of the gaseous phase.
Flow field simulation results exhibited: a) onset of weak secondary flow
accelerated at bend entrance towards the inner wall; b) flow separation zone
development on the convex wall that persisted from the point of onset; c) centrifugal
force concentrated high velocity flow in the direction of the concave wall; d) formation
of vortices throughout the flow domain resulted from rotational (Dean-type) flow; e)
weakened secondary flow assisted the formation of twin vortices in the outflow cross
section; and f) perturbations induced by the bend influenced flow recovery several pipe diameters upstream of the bend. These observations were consistent with those of
previous investigators.
The Lagrangian discrete random walk model, with and without turbulent
dispersion, simulated the dispersed phase behavior, incorrectly. Accurate deposition
predictions in wall-bounded flow require modification of the Eddy Impaction Model
(EIM). Thus, to circumvent shortcomings of the EIM, the Lagrangian time scale was
changed to a wall function and the root-mean-square (RMS) fluctuating velocities were
modified to account for the strong anisotropic nature of flow in the immediate vicinity of
the wall (boundary layer). Subsequent computed trajectories suggest a precision that
ranges from 0.1% to 0.7%, statistical sampling error. The aerodynamic mass median
diameter (AMMD) at the inlet (5.5 μm) was consistent with the ARTIST experimental
findings. The geometric standard deviation (GSD) varied depending on the scenario
evaluated but ranged from 1.61 to 3.2. At the outlet, the computed AMMD (1.9 μm) had
GSD between 1.12 and 2.76. Decontamination factors (DF), computed based on
deposition from trajectory calculations, were just over 3.5 for the bend and 4.4 at the
outlet. Computed DFs were consistent with expert elicitation cited in NUREG-1150 for
aerosol retention in steam generators.
|
679 |
In-situ Synthesis and Luminescence Emission of Non-fully Conjugated Heterocyclic Aromatic Random Copolymers and Multi-wall Carbon Nanotube CompositesHsu, Yi-long 08 July 2004 (has links)
Opto-electronics of non-fully conjugated molecules was demonstrated successfully in this research as light emitting diodes (LEDs). A series of benzoxazole poly[2,2-(m-2-hydroxyl phenylene)-4-4¡¦-hexafluoroisopro- pane-bibenzoxazoles] (6F-PBO-OH, Am) and benzimidazole poly[2,2¡¦- (2-hydroxy-o-phenylene)-5,5¡¦-bibenzimiazole] (OH-Pbi, B(1-m)) were copolymerized for coil-like non-fully conjugated poly-(Am-co-B(1-m)) for luminescence investigation.
UV-Vis absorption of the non-fully conjugated copolymers showed superposition of individual absorption response from the two chemical components of the copolymer. However, the photoluminescence (PL) and the electroluminescence (EL) emissions had a red shift with increasing OH-Pbi content. It seemed to suggest that OH-Pbi was more charge delocalized than 6F-PBO-OH. In mono-layer LEDs, the diode threshold voltages were about at 2 ~ 3 V and the EL showed a green emission. Tunable emission was not observed in varying the m value of the copolymers.
Composites of copolymer, poly(Am-co-B(1-m)) and multi-wall carbon nanotube (MWNT) were in-situ synthesized for mono-layer LED fabrication. Few MWNT aggregation was observed via the field-emission scanning electron microscopy. It was a success in dispersing MWNT in the copolymers. There was a red shift with MWNT addition in the PL and the EL emissions. The diode threshold voltages were about at 2 ~ 5 V and the EL emission still showed a green emission. According to this study, MWNT was inconsequential on the PL and the EL emissions of the copolymers up to 2 wt. %.
|
680 |
White Light Emitting Diodes of Non-fully Conjugated Coil-like Polymer Doped with Derivatized Multi-wall Carbon NanotubesChang, Yi-jyun 28 July 2006 (has links)
Luminescent emission of non-fully conjugated homopolymers was successfully demonstrated as light emitting diodes (LEDs) in this research. Coil-like heterocyclic aromatic poly[2,2-(2,5-dialkyloxyphenylene)-4-4¡¦-hexafluoroisopropanebibenzoxazo- les] (6F-PBO-CnOTpA, with n = 10, 15, and 20) was synthesized, and polymer composites of 6F-PBO-CnOTpA was in-situ synthesized with acidified multi-wall carbon nanotube (MWNT- COOH).
The non-fully conjugated coil-like heterocyclic aromatic homopolymer was synthesized by reacting 2,2,bis-(3-amino-4-hydroxy[henyl]-hexafluoropropane with 2,5-dialkyloxyterephthalic acid (CnOTpA) for 6F-PBO-CnOTpA, with n = 10, 15, and 20. In addition, MWNT was acidified for connecting the carboxylic group (-COOH) to reduce its aspect ratio and entropy induced aggregation. MWNT-COOH was analyzed using elemental analysis (EA) and viscometry to validate the effects of acidification period. The EA result seemed to suggest that the oxygen content increased, and the carbon and the hydrogen contents decreased with acidification period. The inherent viscosity (£binh) decreased according to acidification period suggesting that the aspect ratio was indeed decreased.
A hole transport layer of PEDOT¡GPSS was applied for multi-layer LEDs,. The LEDs all showed a threshold voltage about 4 V also for the composites of 6F-PBO-CnOTpA in-situ polymerized with MWNT-COOH. The 6F-PBO-CnOTpA LEDs with and without MWNT-COOH showed an electroluminescence emission range of 400 to 750 nm.
|
Page generated in 0.0168 seconds