Fabrication and Optical Properties of Noble Metal Nanostructures

Experimental and theoretical results are presented in Chapters 2, 3, and 4 on the effects of dielectric medium, particle size, and interparticle distance, respectively, on plasmon coupling in two-dimensional arrays of silver nanoparticles. The arrays were fabricated via the self-assembly of single crystal particles from c.a. 46 nm to 287 nm on PVP-modified glass substrates. Spin-coated poly(methylmethacrylate) layers were used to immobilize the particles and prevent their surface aggregation. Varying the thickness of the PMMA layer made it possible to change the average dielectric medium between the particles. UV-Visible spectra of different arrays were compared to the corresponding electron microscope images. It was found that increasing the dielectric function of the medium surrounding the particles promoted the coherent plasmon coupling of the particles. It was also observed that increasing the size of the particles in arrays resulted in red shifting and broadening of the coupled plasmon peak. The peak position against the particle size exhibited a linear trend, providing the possibility to adjust a lambda maximum by selecting an appropriate particle size. Decreasing the interparticle distance resulted in spectral shifting and broadening of the plasmon peak and affected the intensity and sharpness of the peaks. Smaller particles shifted to the red spectral range, where as larger particles shifted in the opposite direction upon decreasing the interparticle distance. The phenomenon known as Surface Enhanced Raman Spectroscopy (SERS) is presented in Chapter 5. An analysis of spectra from 20 different molecules adsorbed on SERS substrates revealed competitive Raman enhancement from different types of molecules simultaneously present on the surface. The observed SERS behavior could not be explained using local field enhancement or charge-transfer models. A different SERS mechanism is proposed based on plasmon-induced electronic coupling between the oscillating electrons in the metal and the electronic system of adsorbed molecules. Chapter 6 continues a discussion of SERS but introduces a new substrate based on the low-pressure air plasma reduction of silver compounds to produce porous nanostructured surfaces. This method is advantageous because substrates are easy to prepare and the silver surface is inherently clean for the adsorption of molecules. Silver chloride was found to be the best compound to make reproducible and stable SERS substrates. SERS activity of the substrates was tested using L-tryptophan, 4-mercaptobenzoic acid, and adenine

Determination of Iron(II) Concentrations in Seawater Using Flow Injection Analysis and Chemiluminescence

Phytoplankton are a major consumer of carbon dioxide. In theory, if phytoplankton are limited in number, more carbon dioxide will be present in the atmosphere and contribute to the greenhouse effect. An increased concentration of iron would, therefore, promote phytoplankton blooms that would consume carbon dioxide. There would then be less carbon dioxide in the atmosphere to prevent heat from radiating away from earth. In 1996, an iron seeding experiment was performed in the open ocean to determine whether phytoplankton density would be increased. Phytoplankton rapidly increased in number. The research project results suggested that iron seeding the polar oceans would cause atmospheric carbon dioxide to decrease by as much as 10%.19 Decreasing atmospheric carbon dioxide is beneficial because over abundance of this substance in the atmosphere causes the Green House Effect. Carbon dioxide prevents radiant heat from leaving earth, thereby increasing the overall temperature.Iron can be present in ion form or metal form. The ion forms come in two ways: either iron (II) or iron(III). It is the iron (II) that is the important nutrient for phytoplankton and the iron being assessed. lron(III), however, forms an organic complex that is used by protozoan and . I zooplankton as an uptake nutrient.1 The development of special iron (II) defecting systems would allow a better understanding of the relationship between iron(II) concentrations and phytoplankton growth. Currently, the relationship is poorly understood among scientists. Knowing the iron (II) concentrations will, therefore, enhance our knowledge of the biochemical processes in ocean waters

Marjorie Kinnan Rawlings Society Officers and Trustees Meeting June 23, 1989

Agenda and meeting notes for the June 23, 1989 meeting of the officers and trustees. Dr. Saffy – Secretary, Marjorie Kinnan Rawlings Society

Smoothing consumption across households and time : essays in development economics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 159-163).This thesis studies two strategies that households may use to keep their consumption smooth in the face of fluctuations in income and expenses: credit (borrowing and savings) and insurance (state contingent transfers between households). The first chapter asks why insurance among households in rural Thai villages is incomplete. The second chapter analyzes the impacts of micro-credit. The third chapter examines the interaction between interpersonal insurance and access to savings. The first chapter is motivated by the observation that interpersonal insurance within villages is an important source of insurance, yet consumption, while much smoother than income, is not completely smooth. That is, insurance is incomplete. This chapter attempts to identify the cause of this incompleteness. Existing research has suggested three possibilities: limited commitment-the inability of households to commit to remain within an insurance agreement; moral hazard-the need to give households incentives to work hard; and hidden income-the inability of households to verify one another's incomes. I show that the way in which "history" matters can be used to distinguish insurance constrained by hidden income from insurance constrained by limited commitment or moral hazard. This history dependence can be tested with a simple empirical procedure: predicting current marginal utility of consumption with the first lag of marginal utility and the first lag of income, and testing the significance of the lagged income term. This test is implemented using panel data from households in rural Thailand. The results are consistent with insurance constrained by hidden income, rather than limited commitment or moral hazard. I test the robustness of this result to measurement error using instrumental variables and by testing over-identifying restrictions on the reduced form equation for consumption. I test robustness to the specification of the utility function by nonparametric ally estimating marginal utility. The results suggest that constraints arising from private information about household income should be taken into account when designing safety net and other policies. My second chapter (co-authored with Abhijit Banerjee, Esther Duflo and Rachel Glennerster) uses a randomized trial to analyze the impacts of micro credit in urban South India. We find that more new businesses are created in areas where a micro credit branch opens. Existing business owners increase their spending on durable goods but not non-durable consumption. Among households that did not have a business before the program began, those with high estimated propensity to start a business reduce non-durable consumption and increase spending on durables in treated areas. Those with low estimated propensity to start a business increase non-durable consumption and spend no more on durables. This suggests that some households use micro credit to pay part of the fixed cost of starting a business, some expand an existing business, and others pay off more expensive debt or borrow against future income. We find no effects on health, education, or women's empowerment. My third dissertation chapter (co-authored with Arun Chandrasekhar and Horacio Larreguy) is motivated by the observation that the ability of community members to insure one another may be significantly reduced when community members also have the ability to privately save some of their income. We conducted a laboratory experiment in rural South India to examine the impact of savings access on informal insurance. We find that transfers between players are reduced when savings is available, but that, on average, players smooth their consumption more with savings than without. We use social network data to compute social distance between pairs, and show that limited commitment constraints significantly limit insurance when risk-sharing partners are socially distant, but not when pairs are closely connected. For distant pairs, access to savings helps to smooth income risk that is not insured interpersonally.by Cynthia Georgia Kinnan.Ph.D

The miracle of microfinance? Evidence from a randomized evaluation

This paper reports on the first randomized evaluation of the impact of introducing the standard microcredit group-based lending product in a new market. In 2005, half of 104 slums in Hyderabad, India were randomly selected for opening of a branch of a particular microfinance institution (Spandana) while the remainder were not, although other MFIs were free to enter those slums. Fifteen to 18 months after Spandana began lending in treated areas, households were 8.8 percentage points more likely to have a microcredit loan. They were no more likely to start any new business, although they were more likely to start several at once, and they invested more in their existing businesses. There was no effect on average monthly expenditure per capita. Expenditure on durable goods increased in treated areas, while expenditures on “temptation goods” declined. Three to four years after the initial expansion (after many of the control slums had started getting credit from Spandana and other MFIs ), the probability of borrowing from an MFI in treatment and comparison slums was the same, but on average households in treatment slums had been borrowing for longer and in larger amounts. Consumption was still no different in treatment areas, and the average business was still no more profitable, although we find an increase in profits at the top end. We found no changes in any of the development outcomes that are often believed to be affected by microfinance, including health, education, and women’s empowerment. The results of this study are largely consistent with those of four other evaluations of similar programs in different contexts.This paper updates and supersedes the 2010 version, which reported results using one wave of endline surveys. The authors wish to extend thanks to Spandana, especially Padmaja Reddy whose commitment to understanding the impact of microfinance made this project possible, and to numerous seminar audiences and colleagues for insightful suggestions. The Centre for Micro Finance at IFMR oversaw the experiment and the data collection. Aparna Dasika and Angela Ambroz provided excellent assistance in Hyderabad. Justin Oliver at the Centre for Micro Finance and Annie Duflo at Initiatives for Poverty Action shared valuable advice and logistical support. Adie Angrist, Leonardo Elias, Shehla Imran, Seema Kacker, Tracy Li, Aditi Nagaraj and Cecilia Peluffo provided excellent research assistance. ICICI provided financial support. Datasets for both waves of data used in this paper are available at http://www.centre-for-microfinance.org/publications/data/

The Miracle of Microfinance? Evidence from a Randomized Evaluation

This paper reports results from the randomized evaluation of a group-lending microcredit program in Hyderabad, India. A lender worked in 52 randomly selected neighborhoods, leading to an 8.4 percentage point increase in takeup of microcredit. Small business investment and profits of preexisting businesses increased, but consumption did not significantly increase. Durable goods expenditure increased, while "temptation goods" expenditure declined. We found no significant changes in health, education, or women's empowerment. Two years later, after control areas had gained access to microcredit but households in treatment area had borrowed for longer and in larger amounts, very few significant differences persist.Vanguard Charitable Endowment ProgramSpandana FoundationMassachusetts Institute of Technology. Abdul Latif Jameel Poverty Action La

Expanding Indian public health insurance above the poverty line

Since 2008 India’s public health insurance policy has covered the poorest quarter of the population, and the government wants to expand the policy to include households above the poverty line. Disentangling the health and financial effects of the policy is vital to establishing a cost-effective expansion of eligibility for this insurance