Alexandros G. Rigas

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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)
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)
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)
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)
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)