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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 topological objects: the Blakers-Massey element (a generator of π6(S)) and an exotic (i.e. not isotopic to the identity) diffeomorphism of S6 (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)

- 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)

- 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… (More)

- 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)

- George J. Karavasilis, Alexandros G. Rigas
- 2007 15th European Signal Processing Conference
- 2007

In this work we apply spectral analysis techniques of bivariate stationary point processes for the estimation of the cross-correlation (CC). This is used for the study of a component of the neurophysiological system called muscle spindle. We are interested in the effect of different stimuli to the function of the muscle spindle by recording the response… (More)

- 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.

In this work we present two algorithms for the estimation of the phase of a neuroelectric system of point processes using the third-order spectral density function of the output. The neuroelectric system, which is called muscle spindle, plays an important role in the initiation of the movement and the maintenance of the posture. The system can be modelled… (More)

- Petros T Damos, Nikos T Papadopoulos, Alexandros Rigas, Matilda Savopoulou-Soultani
- Journal of theoretical biology
- 2011

In this work an information theory approach is presented for measuring structural variability during insect metamorphosis. Following a self-organizational perspective, the underlying assumption is that an insect pupa is a cybernetic bio-system, which displays a homeostatic control during its metamorphosis. The description of structural variability was based… (More)