Enhancement of field emission from multistage structure of carbon nanotube arrays

The field emission measurements for the multistage structured nanotubes (i.e., thin-multiwall and single wall carbon nanotubes grown on multiwall carbon nanotubes) were carried out and a low turn-on field of ~0.45 V/ μm, high emission current of 450 μA at a field of IV/μm and a large field enhancement factor of ~26200 were obtained. The thin multiwall carbon nanotubes (thin-MWNTs) and single wall carbon nanotubes (SWNTs) were grown on the regular arrays of vertically aligned multi wall carbon nanotubes (MWNTs) on porous silicon substrate by Chemical Vapor Deposition (CVD) method. The thin-MWNTs and SWNTs grown on MWNTs in this way have a multistage structure which gives higher enhancement of the electric field and hence the electron field emission.

Robust and high current cold electron source based on carbon nanotube field emitters and electron multiplier microchannel plate

The aim of this research was to demonstrate a high current and stable field emission (FE) source based on carbon nanotubes (CNTs) and electron multiplier microchannel plate (MCP) and design efficient field emitters. In recent years various CNT based FE devices have been demonstrated including field emission displays, x-ray source and many more. However to use CNTs as source in high powered microwave (HPM) devices higher and stable current in the range of few milli-amperes to amperes is required. To achieve such high current we developed a novel technique of introducing a MCP between CNT cathode and anode. MCP is an array of electron multipliers; it operates by avalanche multiplication of secondary electrons, which are generated when electrons strike channel walls of MCP. FE current from CNTs is enhanced due to avalanche multiplication of secondary electrons and in addition MCP also protects CNTs from irreversible damage during vacuum arcing. Conventional MCP is not suitable for this purpose due to the lower secondary emission properties of their materials. To achieve higher and stable currents we have designed and fabricated a unique ceramic MCP consisting of high SEY materials. The MCP was fabricated utilizing optimum design parameters, which include channel dimensions and material properties obtained from charged particle optics (CPO) simulation. Child Langmuir law, which gives the optimum current density from an electron source, was taken into account during the system design and experiments. Each MCP channel consisted of MgO coated CNTs which was chosen from various material systems due to its very high SEY. With MCP inserted between CNT cathode and anode stable and higher emission current was achieved. It was ∼25 times higher than without MCP. A brighter emission image was also evidenced due to enhanced emission current. The obtained results are a significant technological advance and this research holds promise for electron source in new generation lightweight, efficient and compact microwave devices for telecommunications in satellites or space applications. As part of this work novel emitters consisting of multistage geometry with improved FE properties were was also developed.

Reducing Health Disparities: Medical advice and health behavior of minorities with diabetes

OBJECTIVE: to examine the relationships among reported medical advice, diabetes education, health insurance and health behavior of individuals with diabetes by race/ethnicity and gender. METHOD: Secondary analysis of data (N = 654) for adults ages > or = 21 years with diabetes acquired through the National Health and Nutrition Examination Survey (NHANES) for the years 2007-2008 comparing Black, non-Hispanics (BNH) and Mexican-Americans (MA) with White, non-Hispanics (WNH). The NHANES survey design is a stratified, multistage probability sample of the civilian noninstitutionalized U.S. population. Sample weights were applied in accordance with NHANES specifications using the complex sample module of IBM SPSS version 18. RESULTS: The findings revealed statistical significant differences in reported medical advice given. BNH [OR = 1.83 (1.16, 2.88), p = 0.013] were more likely than WNH to report being told to reduce fat or calories. Similarly, BNH [OR = 2.84 (1.45, 5.59), p = 0.005] were more likely than WNH to report that they were told to increase their physical activity. Mexican-Americans were less likely to self-monitor their blood glucose than WNH [OR = 2.70 (1.66, 4.38), p < 0.001]. There were differences by race/ethnicity for reporting receiving recent diabetes education. Black, non-Hispanics were twice as likely to report receiving diabetes education than WNH [OR = 2.29 (1.36, 3.85), p = 0.004]. Having recent diabetes education increased the likelihood of performing several diabetes self-management behaviors independent of race. CONCLUSIONS: There were significant differences in reported medical advice received for diabetes care by race/ethnicity. The results suggest ethnic variations in patient-provider communication and may be a consequence of their health beliefs, patient-provider communication as well as length of visit and access to healthcare. These findings clearly demonstrate the need for government sponsored programs, with a patient-centered approach, augmenting usual medical care for diabetes. Moreover, the results suggest that public policy is needed to require the provision of diabetes education at least every two years by public health insurance programs and recommend this provision for all private insurance companies