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Updated: 34 min 24 sec ago

Shear-Induced Aggregation Dynamics in a Polymer Microrod Suspension

Thu, 01/08/2015 - 15:30
Shear-Induced Aggregation Dynamics in a Polymer Microrod Suspension A non-Brownian suspension of micron scale rods is found to exhibit reversible shear-driven formation of disordered aggregates resulting in dramatic viscosity enhancement at low shear rates. Aggregate formation is imaged at low magnification using a combined rheometer and fluorescence microscope system. The size and structure of these aggregates are found to depend on shear rate and concentration, with larger aggregates present at lower shear rates and higher concentrations. Quantitative measurements of the early-stage aggregation process are modeled by a collision driven growth of porous structures which show that the aggregate density increases with a shear rate. A Krieger-Dougherty type constitutive relation and steady-state viscosity measurements are used to estimate the intrinsic viscosity of complex structures developed under shear. Higher magnification images are collected and used to validate the aggregate size versus density relationship, as well as to obtain particle flow fields via PIV. The flow fields provide a tantalizing view of fluctuations involved in the aggregation process. Interaction strength is estimated via contact force measurements and JKR theory and found to be extremely strong in comparison to shear forces present in the system, estimated using hydrodynamic arguments. All of the results are then combined to produce a consistent conceptual model of aggregation in the system that features testable consequences. These results represent a direct, quantitative, experimental study of aggregation and viscosity enhancement in rod suspension, and demonstrate a strategy for inferring inaccessible microscopic geometric properties of a dynamic system through the combination of quantitative imaging and rheology. Ph.D.

Gold Nanoparticle Decorated Carbon Nanotube Field Effect Transistors for Glucose and Gas Sensing

Thu, 01/08/2015 - 15:30
Gold Nanoparticle Decorated Carbon Nanotube Field Effect Transistors for Glucose and Gas Sensing The research presented in this thesis focuses on the fabrication, functionalization and characterization of carbon nanotube field effect transistors (CNTFETs) with gold (Au) nanoparticles for gas and glucose sensing applications.; Carbon nanotube field effect transistors are made of an individual carbon nanotube (CNT) in this work. Carbon nanotubes are synthesized using chemical vapor deposition (CVD) on a p-doped silicon/silicon oxide substrate. This process provides mostly single-walled carbon nanotubes (SWCNTs) that are either metallic or semiconducting. Au is deposited onto the carbon nanotube using electron-beam lithography to make source and drain electrodes. Electrical characterization is performed using software controlled pico-amp meter/DC voltage source connecting to a four-probe micromanipulator system.; A simple in-situ electrochemical method to target the deposition of gold, as well as other metallic nanoparticles along a CNTFET is introduced in this research. The transistors are passivated by a thin layer of poly(methyl-methacrylate), or PMMA. Areas of the PMMA along the carbon nanotube are exposed using electron-beam lithography to target the locations where Au nanoparticles need to be placed. An appropriate potential difference is applied between an in-situ sacrificial gold electrode and the CNT, all immersed under a droplet of electrolyte solution. By adjusting the applied voltage and time of deposition, the size of the Au nanoparticle can be controlled from 10 nm to over 100 nm. This method provides better control and is much easier to carry out compared to other site-specific deposition techniques. Such decorated Au nanoparticle/CNTFET heterostructures will allow for a better understanding of CNTFET gas sensing behavior, as well as finding application in site-specific biomolecule anchoring for the development of highly sensitive and selective biosensors, which will be demonstrated in this research work.; This research suggests that when a Au nanoparticle is deposited onto a semiconducting CNT, a local Schottky barrier is created on the CNT side wall. This Schottky barrier changes when exposed to gas molecules, which is the main mechanism for gas sensing of the CNTFET. For glucose detection, Au nanoparticles provide a preferable orientation of the glucose oxidase molecules, which potentially facilitates the electron transfer between glucose oxidase and the CNT. Ph.D.

Mechanism of Gas Sensing in Carbon Nanotube Field Effect Transistors

Thu, 01/08/2015 - 15:30
Mechanism of Gas Sensing in Carbon Nanotube Field Effect Transistors Gas sensors based on carbon nanotubes in the field effect transistor configuration have exhibited impressive sensitivities compared to the existing technologies. However, the lack of an understanding of the gas sensing mechanism in these carbon nanotube field effect transistors (CNTFETs) has impeded setting-up a calibration standard and customization of these nano-sensors for specified gas sensing application. Calibration requires identifying fundamental transistor parameters and establishing how they vary in the presence of a gas and influence the overall sensing behavior. This work focuses on modeling the sensing behavior of a CNTFET in the presence of oxidizing (NO2) and reducing (NH3) gases and determining how each of the transistor parameters, namely: the Schottky barrier height, Schottky barrier width and doping level of the nanotube are affected by the presence of these gases.; Earlier experiments have shown that the carbon nanotube-metal interface is responsible for the observed change in the CNTFET response. The interface consists of the metal contact and the depletion region in the carbon nanotube. A change in the metal work function will change the Schottky barrier height, whereas doping of the depletion region will affect the Schottky barrier width and the doping level of the carbon nanotube. A theoretical model containing these parameters was systematically fitted to the experimental transfer characteristics for different concentrations of NO2 and NH3. A direct correlation between the measured changes in the CNTFET saturated conductance and the Schottky barrier height was found. These changes are directly related to the changes in the metal work function of the electrodes that I determined experimentally, independently, with a Kelvin probe system. The overall change in the CNTFET characteristics were explained and quantified by also including changes due to doping from molecules adsorbed at the carbon nanotube-metal interface through the parameters Schottky barrier width and the doping level. Ph.D.

CIRS Newsletter 17

Sun, 11/30/2014 - 02:41
CIRS Newsletter 17 Center for International and Regional Studies

Water, State Power, and Tribal Politics in the GCC: The Case of Kuwait and Abu Dhabi

Sun, 11/30/2014 - 02:37
Water, State Power, and Tribal Politics in the GCC: The Case of Kuwait and Abu Dhabi Lambert, Laurent A. This paper shows that the GCC cities’ remarkable capacity to provide water to all their inhabitants despite the regional aridity should not be explained solely by apolitical factors such as the availability of desalination technologies and massive energy resources. Although acknowledging their importance, this paper demonstrates that the historical evolutions and achievements of the water sectors in Abu Dhabi and Kuwait city over the twentieth century are first and foremost the product of local and regional politics, and of reformist leaders’ agency at various times. Major changes in water governance can also be seen as a tool for, and as a signifier of, broader state reforms and changing politics. After independence, the manufacturing,subsidizing, and massive allocation of desalinated water were part of a political strategy aimed at redistributing oil rent to facilitatethe tribes’ allegiance to the regimes, and to legitimize the increasing power of the new states. By contrast, the region’s recent trend of water privatizations, as in Abu Dhabi, Doha, and Riyadh, for instance,represents a strategy of gradually streamlining the rentier states and liberalizing their economies with a post-rentier perspective.

Unemployment and household formation

Thu, 11/27/2014 - 05:57
Unemployment and household formation Ebrahim, Amina; Woolard, Ingrid; Leibbrandt, Murray In comparison to other continents, Africa has received little scholarly attention with regard to household composition. Household composition is endogenous to a variety of welfare issues and little is understood about the determinants of this composition. Understanding the household composition and formation decision may improve our understanding of how the unemployed gain access to resources and how household composition could provide a safety net to the unemployed. However, increasingly, more work is surfacing around the topic in South Africa.

Determinants of life satisfaction among race groups in South Africa

Thu, 11/27/2014 - 05:18
Determinants of life satisfaction among race groups in South Africa Ebrahim, Amina; Botha, Ferdi; Snowball, Jen Economic indicators, like gross domestic product per capita, are commonly used as indicators of welfare. However, they have a very limited and narrow scope, excluding many potentially important welfare determinants, such as health, relative income and religion – not surprising since they were not designed to fill this role. As a result, there is growing acceptance, and use of, subjective measures of well-being (called ‘happiness’ or ‘life satisfaction’, often used interchangeably) both worldwide and in South Africa. Happiness economics does not propose to replace income-based measures of well-being, but rather attempts to complement them with broader measures, which can be important in making policy decisions that optimise societal welfare. This paper tests for differences in subjective well-being between race groups in South Africa, and investigates the determinants of self-rated life satisfaction for each group. Using the 2008 National Income Dynamics Study data, descriptive methods (analysis of variance) and an ordered probit model are applied. Results indicate that reported life satisfaction differs substantially among race groups, with black South Africans being the least satisfied group despite changes since the advent of democracy in 1994. Higher levels of educational attainment increased satisfaction for the whole sample, and women (particularly black women) are generally less satisfied than men. As found in many other studies, unemployed people have lower levels of life satisfaction than the employed, even when controlling for income and relative income. The determinants of life satisfaction are also different for each race group: white South Africans attach greater importance to physical health, whereas employment status and absolute income matter greatly for black people. For coloured people and black people, positional status (as measured by relative income) is an important determinant of well-being, with religious involvement contributing significantly to the well-being of Indian people. http://dx.doi.org/10.1080/0376835X.2013.797227

Ali Gheissari and Vali Nasr. Democracy in Iran

Tue, 10/21/2014 - 14:43
Ali Gheissari and Vali Nasr. Democracy in Iran

EU-GCC Relations: Dynamics, patterns and perspective

Tue, 10/21/2014 - 14:43
EU-GCC Relations: Dynamics, patterns and perspective

Perspectives on the Guaranteed Income, Part I

Tue, 10/21/2014 - 14:43
Perspectives on the Guaranteed Income, Part I A Review of Six Books on Guaranteed Income: Arguing for Basic Income: Ethical Foundations for a Radical Reform by Philippe Van Parijs; A Review of Six Books on Guaranteed Income: Real Freedom for All: What (If Anything) Can Justify Capitalism? by Philippe Van Parijs; A Review of Six Books on Guaranteed Income: The Benefit of Another's Pains: Parasitism, Scarcity, Basic Income by Gijs van Donselaar; A Review of Six Books on Guaranteed Income: The $30,000 Solution: A Guaranteed Annual Income for Every American by Robert R. Schutz; A Review of Six Books on Guaranteed Income: "And Economic Justice for All": Welfare Reform for the 21st Century by Michael L. Murray; A Review of Six Books on Guaranteed Income: The National Tax Rebate: A New America with Less Government by Leonard M. Greene

Transnational Media, Regional Politics and State Security

Tue, 10/21/2014 - 14:43
Transnational Media, Regional Politics and State Security Saudi Arabia is a crucially important media player in the Middle East, commanding modern, sophisticated and far-reaching media systems. Driving the Saudi media hegemony is what may be loosely termed "a security imperative" which is tightly connected to internal dynamics, geopolitical considerations and regional rivalries. Empowered with its oil wealth, Saudi Arabia pursued a dual media strategy, operating state-controlled and circumscribed domestic media systems which insulate the population from undesired external influences and uphold the religious sensibility of the kingdom while developing decentralized, open and modern transnational media systems abroad capable of safeguarding the kingdom's interests and promoting its foreign policy. Instrumental as it may be in the kingdom's comprehensive security approach, though, the media have proven to be an inordinately complex asset. Although remarkable in many respects, the liberalization of Saudi media engendered a number of conflictual dynamics which are potentially consequential.

Dal Seung Yu. The Role of Political Culture in Iranian Political Development

Tue, 10/21/2014 - 14:43
Dal Seung Yu. The Role of Political Culture in Iranian Political Development

Perspectives on the Guaranteed Income, Part II

Tue, 10/21/2014 - 14:43
Perspectives on the Guaranteed Income, Part II A Review of Nine Books on the Guaranteed Income: Freedom and Security: An Introduction to the Basic Income Debate by Tony Fitzpatrick; A Review of Nine Books on the Guaranteed Income: Basic Income: Economic Security for All Canadians by Sally Lerner; Charles M. A. Clark; W. Robert Needham; A Review of Nine Books on the Guaranteed Income: The Stakeholder Society by Bruce Ackerman; Anne Alstott; A Review of Nine Books on the Guaranteed Income: Socioeconomic Democracy: An Advanced Socioeconomic System by Robley E. George; A Review of Nine Books on the Guaranteed Income: Stumbling towards Basic Income: The Politics for Tax-Benefit Integration by Bill Jordan; Phil Agulnik; Duncan Burbidge; Stuart Duffin; A Review of Nine Books on the Guaranteed Income: Healing Politics: Citizen Policies and the Pursuit of Happiness by Steve Shafarman; A Review of Nine Books on the Guaranteed Income: Basic Income on the Agenda: Policy Objectives and Political Chances by Loek Groot; Robert Jan van der Veen; A Review of Nine Books on the Guaranteed Income: Daily Bread, the Story of Jasper's Box by Stephen C. Clark; A Review of Nine Books on the Guaranteed Income: What's Wrong with a Free Lunch? by Joel Rogers; Joshua Cohen

Utraque Unum 2:2 (2009)

Fri, 10/17/2014 - 13:51
Utraque Unum 2:2 (2009) Schall, James Some articles redacted due to copyright restrictions. Please contact digitalscholarship@georgetown.edu for more information.

Georgetown Public Policy Review Volume 10 Number 2

Wed, 10/15/2014 - 14:48
Georgetown Public Policy Review Volume 10 Number 2

Georgetown Public Policy Review Volume 8 Number 2

Wed, 10/15/2014 - 14:47
Georgetown Public Policy Review Volume 8 Number 2

Georgetown Public Policy Review Number 7 Volume 1

Wed, 10/15/2014 - 14:45
Georgetown Public Policy Review Number 7 Volume 1

Fragile Politics: Weak States in the Greater Middle East

Tue, 10/14/2014 - 10:11
Fragile Politics: Weak States in the Greater Middle East Kamrava, Mehran; Schmitz, Charles; Phillips, Sarah; Esser, Daniel; Wehrey, Frederic; Mikaelian, Shoghig; Salloukh, Bassel F.; Abusharaf, Rogaia; de Waal, Alex; Babar, Zahra; Osman, Dwaa; Robinson, Glenn E.; Brand, Laurie; McGillivray, Mark; Feeny, Simon; De Silva, Ashton This CIRS research initiative on weak states in the Middle East begins with a critical analysis of current definitions and terminology of weak and fragile states, scrutinizing the political implications of the prevailing discourse within the setting of the broader Middle East. The research also examines the domestic, regional, and global causes and consequences for the Middle East of the “fragility” of states stretching from Afghanistan and Pakistan in the east to Libya in the west. Employing multidisciplinary perspectives, the Center for International and Regional Studies examines the causes and implications of conceptual notions of state fragility across the region in relation to areas such as politics and security, economics and natural resources, intra- and inter-state relations, migration and population movements, and the broader regional and global political economies.

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