Materials research at national aeronautical laboratory (contributions of S Ramaseshan)

Materials research programmes of the National Aeronautical Laboratory and Prof. Ramaseshan’s contributions to these are presented in this article.     

Optimal blood pressure control in treated hypertensive patients. Report from the Department of Health Hypertension Care Computing Project (DHCCP)

BACKGROUND: We wished to determine the range of treated systolic (SBP) and diastolic blood pressure (DBP) associated with the best survival in hypertensive patients. METHODS AND RESULTS: We conducted a cohort study of patients enrolled in the DoH Hypertension Care Computer Project. Five specialist hypertension clinics (95% of patients) and general practitioners (5%) followed 6214 patients (3070 men and 3144 women) with an average age of 52 years for a mean of 107 months. Total, cardiovascular, ischemic heart disease, (IHD) and stroke mortality were the outcome measures. Age-adjusted relative hazard rates were calculated giving the effect on mortality of systolic or diastolic pressure being higher by 1 mm Hg. In men the optimal level of SBP for all four measures of mortality was the lowest pressure range observed, 92 to 133 mm Hg (median 127). For women the treated SBP range of 96 to 148 mm Hg (median 137) was associated with a low total mortality and also with low to moderate rates for IHD and stroke mortality. Relative hazard rates (P < .001) for IHD mortality were 1.010 for men and 1.013 for women and for stroke mortality were 1.018 and 1.021, respectively. The results were similar in men under and over the age of 60. SBP and DBP tended to be more important in younger than older women. For treated DBP in men, a pressure of 55 to 94 mm Hg (median 87) was associated with a low total mortality. The lowest stroke mortality in men was observed for a DBP range of 55 to 83 mm Hg (median 80) but with a tendency for an increase in IHD mortality. For women DBP < 95 mm Hg (range 55 to 94, median 87) also was associated with a low total mortality. IHD mortality in women was not closely related to treated DBP, relative hazard rate = 1.003, [95% confidence index (CI); 0.990,1.017] but the relative hazard rate for men was 1.011, (95% CI; 1.000, 1.022). The relative hazard rates for treated DBP and stroke were high at 1.035 and 1.028 for men and women, respectively (P < .001). IHD mortality increased in the one third of patients with the greatest fall in DBP on treatment, provided they were not initially in the one-third group with highest untreated DBP. CONCLUSIONS: The best overall survival was associated with a treated SBP of < 134 mm Hg in men and < 149 mm Hg in women and a treated DBP of < 95 mm Hg.     

Starch urea-formaldehyde matrix encapsulation. IV. Influence of solubility and physical state of encapsulant on rate and mechanism of release

The influence of the physical state and solubility of the encapsulant on the rate and mechanism of release and swelling of the cross-linked starch-urea formaldehyde (St-UF) matrix has been studied by encapsulating model organic compounds. The release and swelling data have been analyzed in terms of the generalized equation M_t/M_∞ = ktⁿ applicable for swellable controlled-release systems. This matrix system shows and an inverse relationship of release rate with the cross-link ratio for all the encapsulants studied. The solid encapsulants have n values in the range of 0.22–0.41, indicating a Fickian or anomalous mechanism. Further, the release rate increases with solubility of the encapsulant. The liquid encapsulants have n values in the range of 0.5–1.5, indicating Case II transport mechanism. The release rates for liquid encapsulants are lower by one to three orders of magnitude than those for solid encapsulants and are not influenced by encapsulant solubility. This indicates a polymer chain relaxation-controlled mechanism of release for liquid encapsulants. © 1993 John Wiley & Sons, Inc.     

Growth of hexagonal selenium crystals: Observation of new growth morphologies

In this communication, we report the single crystal growth of selenium by the solution method. We have observed a new mesh-like growth pattern in hexagonal selenium for the first time. Crystals having hexagonal morphology are packed together like hay stick bunches.     

User-friendly dedicated power electronic converter simulator

A user-friendly power electronic simulator for the design and analysis of power electronic circuits is presented. A graphic input interface module called ATOSECG has been developed for the dedicated power electronic converter system simulator ATOSEC5. ATOSECG has tremendously facilitated the interaction of the user with the simulator. Examples of application of the ATOSEC5 simulator for the analysis of a complex multiconverter system are given     

The Web and social networks

The sheer volume of Web data, together with its low signal-to-noise ratio, make it difficult for text-based search engines to locate high-quality pages. Analyzing the links between Web sites has dramatically improved the Web search experience and spawned research into the Web's link structure. This research includes graph-theoretic studies of connectivity, which have shown the Web to have strong similarities with social networks. Self-similarity is pervasive in social networks. While researchers have observed Web self-similarity in other contexts, finding a fractal structure in a graph theoretic setting adds further evidence to the Web's small-world social nature. Thus, researchers seek to explain and exploit the human behavior implicit in the Web's evolving structure. How can we combine the power of Web networks with networks resulting from other human activity? Accomplishing this goal represents knowledge management's key challenge and opportunity.     

Mobility management in integrated wireless-ATM networks

There is an emerging interest in integrating mobile wireless communication with Broadband ISDN based on the ATM technology. Many issues arise when such integration is attempted. This paper addresses the problem of mobility management, i.e., that of tracking the current ATM addresses of mobile terminals and sustaining active ATM connections as mobiles move. The paper presents some architectural options for integrating wireless access to ATM networks and highlights an architecture based oninterworking devices to provide transparent mobility support in existing ATM networks. Location management and handoff solutions for this architecture are then presented. Also, how procedures for multiprotocol transport over ATM networks may be adopted to perform location management is described.A version of this paper appeared in the proceedings of ACM Mobicom '95.     

Synthesizing processed video by filtering temporal relationships

Temporal relationships (motion fields) have been widely exploited by researchers for video processing. Their primary use has been to group pixels in spatiotemporal neighborhoods. Typically, video processing is achieved by filtering, modeling, or analyzing pixels in these neighborhoods. In spite of the widespread use of motion information to process video, rarely are the fields treated as signals, i.e., the temporal relationships are seldom considered as a distinct time series. A notable exception is the generalized autoregressive modeling of these relationships in Rajagopalan et al. (1997). In this work, we present a generalization of finite impulse response filtering applicable to temporal relationships and continue the spirit of that work of treating motion fields as a distinct signal (albeit one that is closely tied to the pixel intensities). Applications presented are preprocessing of video for coding and for noise reduction. Instead of filtering pixels in spatiotemporal neighborhoods directly, we argue that it may be more beneficial to filter the temporal relationships first and then synthesize processed video. Simulations shows MPEG-1 rate gains of up to 20% for coding processed video compared to unprocessed ones where processing leaves the original perceptually unchanged. Noise reduction experiments demonstrate a gain of 0.5 dB at high signal to noise ratios over the best results in the published literature while at low to moderate SNRs, improvements are 0.3 dB lower.