2,632 research outputs found
Lines, Circles, Planes and Spheres
Let be a set of points in , no three collinear and not
all coplanar. If at most are coplanar and is sufficiently large, the
total number of planes determined is at least . For similar conditions and
sufficiently large , (inspired by the work of P. D. T. A. Elliott in
\cite{Ell67}) we also show that the number of spheres determined by points
is at least , and this bound is best
possible under its hypothesis. (By , we are denoting the
maximum number of three-point lines attainable by a configuration of
points, no four collinear, in the plane, i.e., the classic Orchard Problem.)
New lower bounds are also given for both lines and circles.Comment: 37 page
Finite Domain Anomalous Spreading Consistent with First and Second Law
After reviewing the problematic behavior of some previously suggested finite
interval spatial operators of the symmetric Riesz type, we create a wish list
leading toward a new spatial operator suitable to use in the space-time
fractional differential equation of anomalous diffusion when the transport of
material is strictly restricted to a bounded domain. Based on recent studies of
wall effects, we introduce a new definition of the spatial operator and
illustrate its favorable characteristics. We provide two numerical methods to
solve the modified space-time fractional differential equation and show
particular results illustrating compliance to our established list of
requirements, most important to the conservation principle and the second law
of thermodynamics.Comment: 14 figure
Clifford Algebras and Euclid's Parameterization of Pythagorean Triples
We show that the space of Euclid's parameters for Pythagorean triples is
endowed with a natural symplectic structure and that it emerges as a spinor
space of the Clifford algebra , whose minimal version may be
conceptualized as a 4-dimensional real algebra of "kwaternions." We observe
that this makes Euclid's parameterization the earliest appearance of the
concept of spinors. We present an analogue of the "magic correspondence" for
the spinor representation of Minkowski space and show how the Hall matrices fit
into the scheme. The latter obtain an interesting and perhaps unexpected
geometric meaning as certain symmetries of an Apollonian gasket. An extension
to more variables is proposed and explicit formulae for generating all
Pythagorean quadruples, hexads, and decuples are provided.Comment: 22 pages, 7 figures. The sign convention is fixed, one comment on
terminology is adde
The shape of two-dimensional space
Genomics, so fashionable today, is only half of the secret of life. The other half of the secret is shape, form, morphogenesis and metamorphosis. The gene may prescribe what is synthesised, but the proteins appear and operate in a pre-existing environment which they then change. The first step towards life is the appearance of a micelle, a spherical membrane, a surface which separates the world into inside and outside.
We are here concerned with surfaces, with a particular subset of two-dimensional manifolds embedded in three-dimensional Euclidean space, namely the non-self-intersecting, periodic minimal surfaces of cubic symmetry, which separate the world into two regions as an infinite plane would do, but with much more complex topologies. Like the Platonic solids , these cubic surfaces are geometrical absolutes and have distinctive topologies but entail no arbitrary parameters . The objective is to enumerate at least some of these surfaces, for probably an infinite number answer to this description, to draw attention to their geometry and to point to some of their applications and occurrences on various scales between mega-engineering and nano-technology. These objects are solutions looking for problems
A video method for quantifying size distribution, density, and three-dimensional spatial structure of reef fish spawning aggregations
There is a clear need to develop fisheries independent methods to quantify individual sizes, density, and three dimensional characteristics of reef fish spawning aggregations for use in population assessments and to provide critical baseline data on reproductive life history of exploited populations. We designed, constructed, calibrated, and applied an underwater stereo-video system
to estimate individual sizes and three dimensional (3D) positions of Nassau grouper (Epinephelus striatus) at a spawning aggregation site located on a reef promontory on the western edge of Little Cayman Island, Cayman Islands, BWI, on 23 January 2003. The system consists of two free-running camcorders mounted on a meter-long bar and supported by a SCUBA diver. Paired video “stills” were
captured, and nose and tail of individual fish observed in the field of view of both cameras were digitized using image
analysis software. Conversion of these two dimensional screen coordinates to 3D coordinates was achieved through a matrix inversion algorithm and calibration data. Our estimate of mean total length (58.5 cm, n = 29) was in close agreement with estimated lengths from a hydroacoustic
survey and from direct measures of fish size using visual census techniques. We discovered a possible bias in length
measures using the video method, most likely arising from some fish orientations that were not perpendicular with respect to the optical axis of the camera system. We observed 40 individuals occupying a volume of 33.3 m3, resulting in a concentration of 1.2 individuals m–3 with a mean (SD) nearest neighbor distance of 70.0 (29.7) cm. We promote the use of roving diver stereo-videography as a method to assess the size distribution, density, and 3D spatial structure of fish spawning aggregations
Polynomials with symmetric zeros
Polynomials whose zeros are symmetric either to the real line or to the unit
circle are very important in mathematics and physics. We can classify them into
three main classes: the self-conjugate polynomials, whose zeros are symmetric
to the real line; the self-inversive polynomials, whose zeros are symmetric to
the unit circle; and the self-reciprocal polynomials, whose zeros are symmetric
by an inversion with respect to the unit circle followed by a reflection in the
real line. Real self-reciprocal polynomials are simultaneously self-conjugate
and self-inversive so that their zeros are symmetric to both the real line and
the unit circle. In this survey, we present a short review of these
polynomials, focusing on the distribution of their zeros.Comment: Keywords: Self-inversive polynomials, self-reciprocal polynomials,
Pisot and Salem polynomials, M\"obius transformations, knot theory, Bethe
equation
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