139,219 research outputs found
Effect of Mach number on the structure of turbulent spots
No full textDirect numerical simulations have been performed to study the dynamics of isolated turbulent spots in compressible isothermal-wall boundary layers. Results of a bypass transition scenario at Mach 2, 4 and 6 are presented. At all Mach numbers the evolved spots have a leading-edge overhang, followed by a turbulent core and a calmed region at the rear interface. The spots have an upstream-pointing arrowhead shape when visualized by near-wall slices, but a downstream-pointing arrowhead in slices away front the wall. The lateral spreading of the spot decreases substantially with the Mach number, consistent with a growth mechanism based on the instability of lateral shear layers. Evidence for a supersonic (Mach) mode substructure is found in the Mach 6 case, where coherent spanwise structures are observed under the spot overhang region
On the merging of turbulent spots in a supersonic boundary-layer flow
No full textThe complex transition flow physics associated with the merging of turbulent spots in a Mach 2 boundary-layer has been studied using direct numerical simulation. Dynamics of an isolated turbulent spot, merging of laterally displaced spots, and merging of two spots in tandem are considered. The coherent structures associated with the wingtip region of the spot are found to play a major role in destabilising the surrounding laminar fluid. In the merging of laterally displaced spots a strong velocity defect, resulting in unstable inflectional velocity profiles, is observed in the interaction zone. These local inflectional instabilities within the interaction region trigger new large scale coherent structures. During the inline merging, the calmed region behind the tail of the downstream spot is found to suppress the growth of the upstream spot. The upstream spot is ultimately engulfed by the downstream spot
Overlapping product development activities by analysis of information transfer practice
No full textIncludes bibliographical references (p. 21).Funded by the MIT Leaders for Manufacturing Program. Funded by the National Science Foundation's technology management initiative. DDM 9007062Viswanathan Krishnan, Steven D. Eppinger, Daniel E. Whitney
Low Cost Neuromotor Evaluation and Rehabilitation Technologies
No full textiv, 53 p.Under the guidance of Chandramouli Krishnan Ph.D., director of the University of Michigan NeuRRo Lab, the author developed and validated two tools for neuromoter evaluation and rehabilitation: a driving simulator for assessing the braking reaction time in individuals with neuromuscular disability and a neuronavigation system designed to augment transcranial magnetic stimulation sessions. The proprietary software developed as part of the systems was designed to provide low-cost, open source alternatives to existing software. This paper discusses the systems, gives context to the problems that they solve, and offers reflection on the internship experience. Validation results for each system are either under review or close to submission for publication and additionally included herein in their most current and complete forms
Towards a cooperative design methodology : analysis of sequential decision strategies
No full textIncludes bibliographical references (p. 22-24).Supported by the National Science Foundation and the MIT Leaders for Manufacturing Program.Viswanathan Krishnan, Steven D. Eppinger, Daniel E. Whitney
R&D intensity and market valuation of firm: a study of R&D incurring manufacturing firms in India
No full textThe present study examines the impact of R&D expenditure on market valuation of firm using Tobin’s q. The study uses firm level data for Indian manufacturing sector obtained from Prowess database of CMIE for the period 2001-2010. The study forms an unbalanced panel with 326 R&D incurring (reporting) firms and employs Pooled-OLS and fixed effects models to analyze the relationship between R&D investment and firm value. After controlling some firm specific variables the present study finds an inverted U-shaped relationship between R&D intensity and firm value indicating the diminishing marginal return to each rupee spent on R&D. This finding is consistent with the findings of Huang and Liu (2005) for Taiwan and Bracker and Krishnan (2011) for US. It indicates that, R&D investment have a positive impact on the market value of firm at the beginning, but, when the investment exceeds an optimal level, these investments lower the firm value
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Stochastic optimization of electricity transmission : dynamic programming algorithms under uncertainties
No full textThesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 141-144).by Ishwar Krishnan Ashok Sivakumar.M.Eng
Circulating steroid hormone concentrations in postmenopausal women in relation to body size and composition
No full textSteroid hormones are associated with the risk of postmenopausal breast cancer and evidence suggests that increased concentrations of oestrogens from peripheral aromatisation in adipose tissue partly explains the association between body mass index (BMI) and risk of postmenopausal breast cancer. This study examined the associations between circulating concentrations of steroid hormones and anthropometric measurements in a sample of naturally postmenopausal women from the Melbourne Collaborative Cohort Study, not using hormone replacement therapy.
We measured plasma concentration of total oestradiol, oestrone sulphate, dehydroepiandrosterone sulphate, androstenedione, testosterone and sex hormone binding globulin (SHBG) and calculated concentration of free oestradiol. Body measurements included height, weight, BMI, waist circumference, fat mass and fat-free mass, the last two estimated by bioelectrical impedance analysis. BMI was positively associated with both oestrogens and androgens and negatively with SHBG. Fat mass was the principal measure responsible for the association observed between body size and total oestradiol. The associations between oestrone sulphate and androgens and body size were mainly with waist circumference.
The associations between oestrogens and body size were close to null for the first 6 years since menopause and became positive thereafter. Our results are compatible with the hypothesis that after the menopause excess fat mass increases oestrogen concentrations through the peripheral aromatisation of androgens in adipose tissue. This effect requires around 6 years to be detectable by way of circulating steroid hormone levels.Laura Baglietto, Dallas R. English, John L. Hopper, Robert J. MacInnis, Howard A. Morris, Wayne D. Tilley, Kavitha Krishnan and Graham G. Gile
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