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- C. E. DURÁN, A. RIGAS
- 2004

We use the geometry of the geodesics of a certain left-invariant metric on the Lie group Sp(2) to find explicit related formulas for two topo-logical objects: the Blakers-Massey element (a generator of π 6 (S 3)) and an exotic (i.e. not isotopic to the identity) diffeomorphism of S 6 (C. E. Durán, 2001). These formulas depend on two quaternions and their… (More)

- A Rigas, B Rigas, +5 authors D Trichopoulos
- Annals of epidemiology
- 1993

Medical records concerning pediatric or adolescent patients first diagnosed with Crohn's disease or ulcerative colitis in two New York hospitals during a 5-year period (1986 to 1990) were abstracted, and information concerning sex, age, race, birthplace, sibship size, birth order, maternal age at birth, month of birth, duration of breast-feeding, and… (More)

- I. Karanikola, G. C. Anagnostopoulos, A. Rigas
- 1999

We performed a statistical analysis of 290± 500 keV ion data obtained by IMP-8 during the years 1982±1988 within the earth's magnetosheath and analysed in detail some time periods withdistinct ion bursts. These studies reveal the following characteristics for magnetosheath 290±500 keV energetic ions: (a) the occurrence frequency and the ¯ux of ions increase… (More)

- P Kaklamanis, A Rigas, J Giannatos, S Matsas, P Economou
- The New England journal of medicine
- 1975

- George J. Karavasilis, V. K. Kotti, Dimitrios S. Tsitsis, V. G. Vassiliadis, Alexandros G. Rigas
- Computational Statistics & Data Analysis
- 2005

Different statistical methods for the assessment of potential risk factors are discussed, in the case of a complex neurophysiological system, involving binary observations. The first approach describes the use of non-parametric methods, which are based on the cross-product ratio (CPR). The estimates of the CPR are given both in time and frequency domains… (More)

- CARLOS DURÁN, A. RIGAS
- 2006

We construct a new infinite family of models of exotic 7-spheres. These models are direct generalizations of the Gromoll-Meyer sphere. From their symmetries, geodesics and submanifolds half of them are closer to the standard 7-sphere than any other known model for an exotic 7-sphere.

- C Dur´an, A Rigas
- 2008

We present a way of constructing and deforming diffeomorphisms of manifolds endowed with a Lie group action. This is applied to the study of exotic diffeomorphisms and involutions of spheres and to the equivariant homotopy of Lie groups.

- D M Halliday, J R Rosenberg, A Rigas, B A Conway
- Journal of neuroscience methods
- 2009

In one approach to spectral estimation, a sample record is broken into a number of disjoint sections, or data is collected over a number of discrete trials. Spectral parameters are formed by averaging periodograms across these discrete sections or trials. A key assumption in this approach is that of weak stationarity. This paper describes a simple test that… (More)

- V. G. Vassiliadis, Alexandros G. Rigas
- Neurocomputing
- 2009