Development of novel dynamic indentation techniques for soft tissue applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (leaves 141-149).Realistic material models to simulate the behavior of brain tissue at large deformations and high strain rates are necessary when designing equipment to protect against ballistic impacts. Acquiring experimental data for brain tissue response is critical to developing appropriate models. Current in vivo and in situ procedures for testing the material behavior of soft tissues are dominated by indentation techniques. The major challenge for this testing configuration is in finding a unique solution to the "inverse problem" i.e., obtaining material properties that are uniquely defined by the indentation force-displacement response. Much of the information related to the interplay between shear and bulk compliance in the deformation field beneath the indenter is lost when capturing the single force-displacement output. To address this challenge, we propose a material testing technique that follows the well- proven path of conventional indentation methods, but also enriches the signal by acquiring displacement data for an offset, passive surface tracking sensor. We present the results of a finite element (FE) study to demonstrate that the addition of a secondary sensor can help to discern between materials with varying degrees of compressibility. To this end, a large displacement in vivo dynamic indentation surface tracking (DIST) tool was designed and manufactured. This tool incorporates the secondary sensor concept to measure the force-displacement response of brain tissue at strain rates up to 1000%/s. The technique is applied in vitro to measure the response of porcine brain tissue. To select an appropriate constitutive framework for porcine brain tissue in vitro, uniaxial compression tests measuring the corresponding lateral stretch response are performed.(cont.) A three-dimensional large deformation constitutive model for brain tissue is developed. The model accounts for the observed features of the material response including non-linearity, conditioning, hysteresis, and strain-rate dependence. The model is incorporated into an FE simulation of the brain indentation tests performed with the DIST tool. The effectiveness of the DIST as a material-testing tool is assessed.by Asha Balakrishnan.Ph.D

Effect of TiO₂ nanotube length and lateral tubular spacing on photovoltaic properties of back illuminated dye sensitized solar cell

The main objective of this study is to show the effect of TiO2 nanotube length, diameter and intertubular lateral spacings on the performance of back illuminated Dye Sensitized Solar Cells (DSSCs). The present study shows that processing short TiO2 nanotubes with good lateral spacings could significantly improve the performance of back illuminated DSSCs. Vertically aligned, uniform sized diameter TiO2 nanotube arrays of different tube lengths have been fabricated on Ti plates by a controlled anodization technique at different times of 24, 36, 48 and 72 h using ethylene glycol and ammonium fluoride as an electrolyte medium. Scanning Electron Microscopy (SEM) showed formation of nanotube arrays spread uniformly over a large area. X-ray Diffraction (XRD) of TiO2 nanotube layer revealed the presence of crystalline anatase phases. By employing the TiO2 nanotube array anodized at 24 h showing a diameter ∼80 nm and length ∼1•5 μm as the photo-anode for back illuminated DSSCs, a full-sun conversion efficiency (η) of 3•5% was achieved, the highest value reported for this length of nanotubes

Hepatic Stem-like Phenotype and Interplay of Wnt/β-Catenin and Myc Signaling in Aggressive Childhood Liver Cancer

SummaryHepatoblastoma, the most common pediatric liver cancer, is tightly linked to excessive Wnt/β-catenin signaling. Here, we used microarray analysis to identify two tumor subclasses resembling distinct phases of liver development and a discriminating 16-gene signature. β-catenin activated different transcriptional programs in the two tumor types, with distinctive expression of hepatic stem/progenitor markers in immature tumors. This highly proliferating subclass was typified by gains of chromosomes 8q and 2p and upregulated Myc signaling. Myc-induced hepatoblastoma-like tumors in mice strikingly resembled the human immature subtype, and Myc downregulation in hepatoblastoma cells impaired tumorigenesis in vivo. Remarkably, the 16-gene signature discriminated invasive and metastatic hepatoblastomas and predicted prognosis with high accuracy

Can community action improve equity for maternal health and how does it do so? Research findings from Gujarat, India

BACKGROUND: Efforts to work with civil society to strengthen community participation and action for health are particularly important in Gujarat, India, given that the state has resources and capacity, but faces challenges in ensuring that services reach those most in need. To contribute to the knowledge base on accountability and maternal health, this study examines the equity effects of community action for maternal health led by Non-Government Organizations (NGOs) on facility deliveries. It then examines the underlying implementation processes with implications for strengthening accountability of maternity care across three districts of Gujarat, India. Community action for maternal health entailed NGOs a) working with community collectives to raise awareness about maternal health entitlements, b) supporting community monitoring of outreach government services, and c) facilitating dialogue with government providers and authorities with report cards based on community monitoring of maternal health. METHODS: The study combined qualitative data (project documents and 56 stakeholder interviews thematically analyzed) with quantitative data (2395 women's self-reported receipt of information on entitlements and use of services over 3 years of implementation monitored prospectively through household visits). Multivariable logistic regression examined delivery care seeking and equity. RESULTS: In the marginalised districts, women reported substantial increases in receipt of information of entitlements and utilization of antenatal and delivery care. In the marginalized and wealthier districts, a switch from private facilities to public ones was observed for the most vulnerable. Supportive implementation factors included a) alignment among NGO organizational missions, b) participatory development of project tools, c) repeated capacity building and d) government interest in improving utilization and recognition of NGO contributions. Initial challenges included a) confidence and turnover of volunteers, b) complexity of the monitoring tool and c) scepticism from both communities and providers. CONCLUSION: With capacity and trust building, NGOs supporting community based collectives to monitor health services and engage with health providers and local authorities, over time overcame implementation challenges to strengthen public sector services. These accountability efforts resulted in improvements in utilisation of public sector services and a shift away from private care seeking, particularly for the marginalised

U.S. Visa Policy Effects on S&T Participation of Foreign Scientists

Atlanta Conference on Science and Innovation Policy 2009This presentation was part of the session : Science and Innovation Workforc

Contact-type mechanical interfaces for high speed digital interconnects

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 96).The objective of this work was to determine the feasibility of Ball Grid Array (BGA) planarization and to investigate the effects of mechanical contacts on signal integrity for high­speed digital signals. As devices become smaller and clock frequencies increase, new technologies for contacting devices are being developed, especially in the field of semiconductor test. These contactors will be incorporated into a socket or an interconnect used in testing devices or printed circuit boards. The heights of the solder ball leads on BGA packages have a high degree of co-planarity. As BGA pitches become tighter, the requirement for improved co-planarity persists. This thesis shows that through diamond turning techniques, the co-planarity of the solder ball leads can be improved. Planarization of solder balls enables the use and development of rigid interconnects. Interconnections generally have a built in compliance to them to accommodate for co-planarity. Reducing co-planarity eliminates the need for compliant interconnects. Contact mechanics identifies the conical shaped tip as the optimal tip shape, providing the best mechanical connection. The intent of the tip shape investigation is to correlate indentation theory with signal integrity. The electrical performance of the contactor tip is evaluated using the industry standard pogo pin. Mechanical parameters are varied to observe the effect on the signal integrity. At high frequencies, the interconnect provides a vulnerable location for signal losses to occur. A new interconnect design to address the electrical performance of existing designs is introduced. The cantilevered interconnect consists of a coplanar waveguide cross-section. The interconnect is both mechanically and electrically sound. This thesis presents aspects of mechanical contact interfaces for electrical signal testing purposes. It focuses on device interfacing, contactor tip shape, signal integrity and new interconnect designs.by Asha Balakrishnan.S.M

Measuring the Interdisciplinarity of a Federal R&D Program Using Bibliometrics and Science Overlay Maps

Atlanta Conference on Science and Innovation Policy 2011We conducted an assessment of a government R&D program focused on funding potentially transformative research and interdisciplinary research. To better understand the interdisciplinarity of the funded researchers and their associated awarded proposals, we used the integration score technique to measure the interdisciplinarity of this programs awards and researchers compared to awards funded by more traditional mechanisms at the agency. This talk will describe our methodology in more detail

MicroRNA-221: A Fine Tuner and Potential Biomarker of Chronic Liver Injury.

The last decade has witnessed significant advancements in our understanding of how small noncoding RNAs, such as microRNAs (miRNAs), regulate disease progression. One such miRNA, miR-221, has been shown to play a key role in the progression of liver fibrosis, a common feature of most liver diseases. Many reports have demonstrated the upregulation of miR-221 in liver fibrosis caused by multiple etiologies such as viral infections and nonalcoholic steatohepatitis. Inhibition of miR-221 via different strategies has shown promising results in terms of the suppression of fibrogenic gene signatures in vitro, as well as in vivo, in independent mouse models of liver fibrosis. In addition, miR-221 has also been suggested as a noninvasive serum biomarker for liver fibrosis and cirrhosis. In this review, we discuss the biology of miR-221, its significance and use as a biomarker during progression of liver fibrosis, and finally, potential and robust approaches that can be utilized to suppress liver fibrosis via inhibition of miR-221

Alcoholic extract of Wrightia tinctoria leaves and isolates there of afford DNA protection in post irradiated Sprague Dawley rats

Objective: The current study investigates the potential of alcoholic extract of Wrightia tinctoria leaves and its isolates in repairing the DNA damage induced by gamma radiation. Methodology: The ethanolic extract of Wrightia tinctoria (EEWT) the leaves was subjected to in vitro anti oxidant assay by DPPH radical scavenging and hydrogen peroxide scavenging methods. He EEWT was investigated to the Micronucleus assay, spleen colony assay and comet assay in Sprague Dawley rats wherein DNA damage had already been induced by irradiation. Results: The ethanolic extract of Wrightia tinctoria leaves having good antioxidant activity. In the micronucleus assay, a 2 Gy quantum of whole-body gamma radiation significantly enhanced the levels of micronucleated reticulocytes and this induction was substantially reversed in the extract treatment group. Results of the spleen colony assay pointed to the extract's ability to enhance the recovery of the hematopoietic system, in a dose-dependent manner, following 6 Gy gamma irradiation. The decrease in cellular repair index due to enhanced DNA repair was evident from the comet assay parameters. Moreover, the isolates from ethanolic extract of Wrightia tinctoria, when imperiled to DNA protection by in vitro gamma radiation method in plasmid pBR322 DNA, abetted DNA repair at higher dose. Conclusion: The DNA protection afforded is likely attributable to free radical scavenging properties along with a potential for regenerating the immune system through repair of post irradiated DNA