Fabrication, characterization, and micromagnetic analysis of lithographically defined particle arrays for applications in data storage

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references (leaves 101-103).In this thesis, the magnetic behavior of nanostructured ferromagnetic particle arrays are studied by experiments and numerical micromagnetics for ultra-high-density data storage applications. 1 00nm or 200nm period arrays of nanostructured nickel, cobalt, and cobalt phosphorus are fabricated by the techniques of interference lithography combined with evaporation and electrodeposition. The nanomagnet arrays are characterized by bulk magnetometry and magnetic force microscopy. The remanent states of evaporated conical particles and electrodeposited cylindrical particles are studied by micromagnetic simulations and compared with experimental measurements. For electrodeposited particles, the influence of size, aspect ratio and microstructure on switching field is also investigated. Finally, the effect of demagnetizing magnetostatic interactions and switching field spread on the squareness and the shape of hysteresis loops is studied with the help of an Ising-like interaction model. Based on these observations, a stability condition for patterned media is found and used for determining the optimum spacing between nanomagnets.by Minha Hwang.Ph.D

From Online to Mobile: Linking Consumers’ Online Purchase Behaviors with Mobile Commerce Adoption

With the growing popularity of mobile commerce (m-commerce), it becomes vital for both researchers and practitioners to understand consumers’ mobile commerce adoption behavior. In this study, we empirically investigate the drivers of consumers’ mobile commerce adoption behavior based on a cost and benefit framework. Based on consumers\u27 browsing and purchase behaviors at the e-commerce site before the addition of mobile commerce channel, we constructed behavioral proxy variables which capture the underlying cost and benefit of mobile commerce channel relative to the pre-existing e-commerce channel. We collected two large datasets from of a large e-marketplace in South Korea that introduced mcommerce to its existing e-commerce offering in 2011. Based on the analysis of browsing and purchase behaviors of 29,283 subjects over a period of 28 months, we find that the need for ubiquity plays a significant role in the m-commerce adoption decision. The two proxies for ubiquity need— Purchase frequency and Purchase time irregularity—were found to have a positive impact on mcommerce adoption. The results also suggest that search cost influences the decision to adopt mcommerce. Specifically, we find that the consumers who search multi-item or categories at a time, engage in active search, and conduct thorough search, are less likely to adopt m-commerce. Finally, the results show that the risk preference of the consumer is related to the adoption decision. Risk aversion, as measured by the two proxies—Reliance on secure log-in system, and Need for receiving confirmations—lowers the likelihood of m-commerce adoption. These results highlight the importance of the unique features of mobile platform in influencing the consumers’ adoption of m-commerce. We discuss the implications of our findings for academics and practitioners

Estimation of instantaneous and daily net radiation from MODIS data under clear sky conditions: a case study in East Asia

The Moderate Resolution Imaging Spectroradiometer-based net radiation (R N) model was built and applied in East Asia in 2005. Because there have hardly been simple parameterization schemes developed over a large area using remote-sensing technology, the model was aimed to present physical simplicity in complex topography at multiple spatiotemporal scales. The model successfully reproduced the instantaneous R N values obtained at four flux tower sites having individually different ecohydrology. The diurnal cycle of R N was contextually simulated using a simple sine curve to determine the daily and monthly average net radiation. The diurnal R N estimation method was proven to be a reliable model as long as accurate boundary conditions, sunrise and sunset times, for example, were obtained. The monthly average net radiation (MANR) was estimated using the diurnal patterns of the instantaneous R N. Distribution of the monthly R N demonstrated that elevation and latitude were the primary factors affecting the MANR. The proposed R N algorithm turned out to be a promising method for valuable applications in various fields due to systematic simplicity and fewer input parameters.This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (2012-0002516). This research was also supported by a grant (development of spatial mapping for ET and soil moisture using remote sensing data) from the Hydrological Survey Center, Korea. Data were provided by KoFlux from projects funded by the Ministry of Land, Transport and Maritime Affairs, the Korea Forest Research Institute, and the Korea Science and Engineering Foundation

Ecosystem-dynamics link to hydrologic variations for different land-cover types

The soil moisture and evapotranspiration (ET) influence on ecosystem dynamics has been studied only in a limited way owing to the lack of large-scale measurements. The Normalized Difference Vegetation Index (NDVI) data retrieved using the Moderate Resolution Imaging Spectroradiometer (MODIS) was successfully used in this study to identify the ecological relationships that involve soil moisture and ET at 132 sites located on different continents around the world. Optimal relationships exist between NDVI and soil moisture within time lags of 10 days at forest and grassland sites, and 25 days at cropland and shrub land sites. The ecological correlations between NDVI and the hydrological variables are affected mainly by the land-cover type. The densely vegetated areas show shorter time lags for NDVI to ET owing to canopy evaporation and plant transpiration, which are almost simultaneous with NDVI

Shopping Activity at Warehouse Club Stores and Its Competitive and Network-Density Implications

Warehouse club (WC) retailers have typically expanded to new markets using stand‐alone stores, rather than pursuing dense store networks as other (non‐WC) retailers have in the past. While this strategy generates operating efficiencies, it also imposes high travel costs on households to shop, which calls into question WC stores’ resilience to spatial competition from stores operating other formats. We examine this phenomenon by using data on households’ shopping activity across markets served by Costco Wholesale stores. Specifically, we evaluate these stores’ resilience to spatial competition by estimating the share of households’ expenditures relative to travel costs to shop at the stores and comparing this estimate with that for non‐WC stores. Controlling for households’ travel costs across Costco and non‐WC stores, we find that households’ share of expenditures at Costco stores exceeds the share at non‐WC stores by 61%. This suggests that Costco stores have an advantage over non‐WC stores when serving market areas with sparse store networks. Nevertheless, we also find that this advantage diminishes with the distance between Costco stores and households and that there is a finite distance beyond which this advantage disappears. We show that this distance (approximately 21 miles) is an important reference point for the evaluation of spatial competition between Costco stores and other stores and the examination of demand saturation at Costco stores

Demand Externalities from Co-Location Demand Externalities from Co-Location

Abstract We illustrate an approach to measure demand externalities from co-location by estimating household level changes in grocery spending at a supermarket among households that also buy gas at a co-located gas station, relative to those who do not. Controlling for observable and unobserved selection in the use of gas station, we find significant demand externalities; on average a household that buys gas has 7.7% to 9.3% increase in spending on groceries. Accounting for differences in gross margins, the profit from the grocery spillovers is 130% to 150% the profit from gasoline sales. The spillovers are moderated by store loyalty, with the gas station serving to cement the loyalty of store-loyal households. The grocery spillover effects are significant for traditional grocery products, but 23% larger for convenience stores. Thus co-location of a new category impacts both inter-format competition with respect to convenience stores (selling the new category) and intra-format competition with respect to other supermarkets (selling the existing categories)

ONC201 and an MEK Inhibitor Trametinib Synergistically Inhibit the Growth of Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) is a heterogeneous group of estrogen, progesterone, and HER2-negative breast cancers with poor clinical outcomes. The imipridone ONC201 is a G-protein-coupled dopamine receptor D2 modulator and an allosteric agonist of the mitochondrial protease caseinolytic protease P(ClpP), which induces apoptosis. Here, we aimed to develop a novel ONC201-based combination therapy targeting TNBC. We performed a reverse-phase protein array analysis of ONC201-treated/-untreated and -sensitive/-resistant cell lines to identify potential predictive biomarkers. A principal component analysis using measured protein expression levels, the apoptosis score (AS), and heatmaps of all the measured protein and AS-related protein expression levels did not show a clear correlation between the expression levels of a specific protein and ONC201 efficacy. Three-dimensional RNA interference kinome-wide library screening revealed the MAPK and PI3K/Akt pathways as potential synergistic therapeutic partners. The combination with the MEK inhibitor trametinib successfully inhibited the growth of both ONC201-sensitive/-resistant TNBC cell lines. The baseline ClpP level correlated with the efficacy of single-agent ONC201. Single and combination therapy increased caspase 3/7 activity. The predictive biomarkers and a detailed mechanism of synergy beyond an induction of caspase activation should be tested for translation into future studies