The interaction of helical tip and root vortices in a wind turbine wake

Analysis of the helical vortices measured behind a model wind turbine in a water channel are reported. Phase-locked measurements using planar particle image ve- locimetry are taken behind a Glauert rotor to investigate the evolution and breakdown of the helical vortex structures. Existing linear stability theory predicts helical vortex filaments to be susceptible to three unstable modes. The current work presents tip and root vortex evolution in the wake for varying tip speed ratio and shows a breaking of the helical symmetry and merging of the vortices due to mutual inductance between the vortical filaments. The merging of the vortices is shown to be steady with rotor phase, however, small-scale non-periodic meander of the vortex positions is also ob- served. The generation of the helical wake is demonstrated to be closely coupled with the blade aerodynamics, strongly influencing the vortex properties which are shown to agree with theoretical predictions of the circulation shed into the wake by the blades. The mutual inductance of the helices is shown to occur at the same non-dimensional wake distance

Who is Bearing the Cost of the AIDS Epidemic in Asia?

This chapter infers the distribution of AIDS costs in India, Indonesia, and Thailand from data on the costs of detecting and treating AIDS and from information on the nature of different countries health care finance systems and related institutions. The main finding is that the AIDS epidemic will contribute to increased economic inequality in these countries because (a) it is disproportionately affecting low-income groups and (b) public and private institutions that could spread the costs of the epidemic (for example, health, life, disability, and social welfare insurance) are relatively limited and do not reach the majority of the populations. The chapter also develops a new approach to measuring AIDS medical care costs that yields estimates of US $738 per case in India and US$1490 per case in Indonesia. Finally, the chapter discusses the political economy of HIV prevention and speculates that more effective control of the epidemic may result from a system in which the government pays for the medical care costs of AIDS than one in which individuals with AIDS and their families bear most of the costs

Projecting the Number of New AIDS Cases in the U.S.

This paper reviews the two leading methods used to project the number of AIDS cases: back calculation and extrapolation. These methods are assessed in light of key features of the HIV/AIDS epidemic and of data on the epidemic; they are also assessed in terms of the quality of the projections they yield. Our analysis shows that both methods have tended to overproject, often by sizable amounts, the number of AIDS cases in the U.S., especially among homosexual/bisexual males and users of blood and blood products. Our results provide no evidence that the use of AZT and other prophylaxis accounts for these projection errors. Rather, the overprojections appear to be mainly the result of a considerable reduction in the rate of new HIV infection among the gay community starting in 1983-85. A new method for projecting AIDS cases is proposed that exploits knowledge about the process generating AIDS cases and that incorporates readily available information about rates of new HIV infection. This method is far less sensitive to estimates of the incubation distribution than the method of back calculation and is shown, for the two transmission categories studied, to generate far more accurate AIDS case projections through 1990 than those based on the method of extrapolation. Relative to the method of extrapolation, this method projects 22,000 fewer new AIDS cases for 1995 (a 36 percent difference). This method also projects that intravenous drug users will replace homosexual/bisexual men as the dominant transmission category for AIDS

Examining Predictors and Outcomes of Identity Communication in Virtual Teams

Virtual teams play an increasingly important role in the modern economy, and many organizations struggle to overcome the weaknesses inherent in technology-mediated work. Identity communication has been shown to greatly improve individual- and group-level outcomes in offline settings, but these benefits have not been investigated in the context of virtual teams, where mediated interaction can affect the opportunity for identity communication. This research-in-progress paper proposes a theoretical model and experimental design that investigates the predictors and outcomes of identity communication in virtual teams. Our anticipated findings should have important implications for researchers seeking to understand identity communication via technology and for practitioners hoping to improve virtual team communication and collaboration.

Distribution of plasma membrane-associated syntaxins 1 through 4 indicates distinct trafficking functions in the synaptic layers of the mouse retina

BACKGROUND: Syntaxins 1 through 4 are SNAP receptor (SNARE) proteins that mediate vesicular trafficking to the plasma membrane. In retina, syntaxins 1 and 3 are expressed at conventional and ribbon synapses, respectively, suggesting that synaptic trafficking functions differ among syntaxin isoforms. To better understand syntaxins in synaptic signaling and trafficking, we further examined the cell- and synapse-specific expression of syntaxins 1 through 4 in the mouse retina by immunolabeling and confocal microscopy. RESULTS: Each isoform was expressed in the retina and showed a unique distribution in the synaptic layers of the retina, with little or no colocalization of isoforms. Syntaxin 1 was present in amacrine cell bodies and processes and conventional presynaptic terminals in the inner plexiform layer (IPL). Syntaxin 2 was present in amacrine cells and their processes in the IPL, but showed little colocalization with syntaxin 1 or other presynaptic markers. Syntaxin 3 was found in glutamatergic photoreceptor and bipolar cell ribbon synapses, but was absent from putative conventional glutamatergic amacrine cell synapses. Syntaxin 4 was localized to horizontal cell processes in the ribbon synaptic complexes of photoreceptor terminals and in puncta in the IPL that contacted dopaminergic and CD15-positive amacrine cells. Syntaxins 2 and 4 often were apposed to synaptic active zones labeled for bassoon. CONCLUSION: These results indicate that each syntaxin isoform has unique, non-redundant functions in synaptic signaling and trafficking. Syntaxins 1 and 3 mediate presynaptic transmitter release from conventional and ribbon synapses, respectively. Syntaxins 2 and 4 are not presynaptic and likely mediate post-synaptic trafficking

Observations of Binary Stars with the Differential Speckle Survey Instrument. II. Hipparcos Stars Observed in 2010 January and June

The results of 497 speckle observations of Hipparcos stars and selected other targets are presented. Of these, 367 were resolved into components and 130 were unresolved. The data were obtained using the Differential Speckle Survey Instrument at the WIYN 3.5 m Telescope. (The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.) Since the first paper in this series, the instrument has been upgraded so that it now uses two electron-multiplying CCD cameras. The measurement precision obtained when comparing to ephemeris positions of binaries with very well known orbits is approximately 1-2 mas in separation and better than 0°.6 in position angle. Differential photometry is found to be in very good agreement with Hipparcos measures in cases where the comparison is most relevant. We derive preliminary orbits for two systems

17-An Archaeological Survey of the Middle St. Joseph River Valley in St. Joseph County, Michigan

Between 2-19 Jun 86, a team of researchers from Western Michigan University conducted a reconnaissance level survey of a 63.5 km2 transect across the St. Joseph River Valley in Leonidas and Colon Townships, St. Joseph County, Michigan. They gained access to 77 parcels of farmland affording good to excellent surface visibility and aggregating 15.3 km 2 , or 24% of the entire study area. In the process, 87 new archaeological sites were located and recorded; another three sites were recorded on the basis of documentary evidence reviewed during the course of the project. For each of 16 sampling strata evaluated, at least one site attributable to Amerindian occupation was recorded. However, the data on site distribution in the study area show a pronounced tendency for the more impressive sites to concentrate along the course of the St. Joseph, especially near the confluence of Nottawa Creek with the river, and to a lesser extend along the lower reaches of this feeder stream and overlooking Long Lake through which another major tributary, Swan Creek, passes as it flows toward its confluence with the St. Joseph River. In the report which follows, the survey area is briefly described, previously recorded sites are discussed, the research design employed in this survey is outlined, and the results of our efforts are fully presented. The report concludes with comparisons of the data set derived from the 1986 SJVA-I transect with those acquired during similar programs of research in the nearby drainages of the Middle Kalamazoo and Portage Rivers, together with some general statements about the implications of these data for Amerindian subsistence settlement behavior in this area of southwest Michigan. In our recommendations regarding management of archaeological resources in this apparently very rich zone, we mention that as many as 10 sites recorded by the survey team in 1986 may warrant evaluation of their eligibility For listing in the National Register of Historic Places; note our current plans to conduct Phase II investigations at two of these sites in the upcoming field season, with grant support From the Historic Preservation Grant Program administered through the Bureau of History, Michigan Department of State; and comment on the cooperative attitude of area landowners and how good communications between professional archaeologists and property owners in the study area will greatly Facilitate management efforts with respect to the resources as well as make possible future research oriented toward mare intensive evaluation of potentially significant sites in this universe

Cauchy, infinitesimals and ghosts of departed quantifiers

Procedures relying on infinitesimals in Leibniz, Euler and Cauchy have been interpreted in both a Weierstrassian and Robinson's frameworks. The latter provides closer proxies for the procedures of the classical masters. Thus, Leibniz's distinction between assignable and inassignable numbers finds a proxy in the distinction between standard and nonstandard numbers in Robinson's framework, while Leibniz's law of homogeneity with the implied notion of equality up to negligible terms finds a mathematical formalisation in terms of standard part. It is hard to provide parallel formalisations in a Weierstrassian framework but scholars since Ishiguro have engaged in a quest for ghosts of departed quantifiers to provide a Weierstrassian account for Leibniz's infinitesimals. Euler similarly had notions of equality up to negligible terms, of which he distinguished two types: geometric and arithmetic. Euler routinely used product decompositions into a specific infinite number of factors, and used the binomial formula with an infinite exponent. Such procedures have immediate hyperfinite analogues in Robinson's framework, while in a Weierstrassian framework they can only be reinterpreted by means of paraphrases departing significantly from Euler's own presentation. Cauchy gives lucid definitions of continuity in terms of infinitesimals that find ready formalisations in Robinson's framework but scholars working in a Weierstrassian framework bend over backwards either to claim that Cauchy was vague or to engage in a quest for ghosts of departed quantifiers in his work. Cauchy's procedures in the context of his 1853 sum theorem (for series of continuous functions) are more readily understood from the viewpoint of Robinson's framework, where one can exploit tools such as the pointwise definition of the concept of uniform convergence. Keywords: historiography; infinitesimal; Latin model; butterfly modelComment: 45 pages, published in Mat. Stu