90,908 research outputs found
Sweeping an oval to a vanishing point
Given a convex region in the plane, and a sweep-line as a tool, what is best
way to reduce the region to a single point by a sequence of sweeps? The problem
of sweeping points by orthogonal sweeps was first studied in [2]. Here we
consider the following \emph{slanted} variant of sweeping recently introduced
in [1]: In a single sweep, the sweep-line is placed at a start position
somewhere in the plane, then moved continuously according to a sweep vector
(not necessarily orthogonal to the sweep-line) to another parallel end
position, and then lifted from the plane. The cost of a sequence of sweeps is
the sum of the lengths of the sweep vectors. The (optimal) sweeping cost of a
region is the infimum of the costs over all finite sweeping sequences for that
region. An optimal sweeping sequence for a region is one with a minimum total
cost, if it exists. Another parameter of interest is the number of sweeps.
We show that there exist convex regions for which the optimal sweeping cost
cannot be attained by two sweeps. This disproves a conjecture of Bousany,
Karker, O'Rourke, and Sparaco stating that two sweeps (with vectors along the
two adjacent sides of a minimum-perimeter enclosing parallelogram) always
suffice [1]. Moreover, we conjecture that for some convex regions, no finite
sweeping sequence is optimal. On the other hand, we show that both the 2-sweep
algorithm based on minimum-perimeter enclosing rectangle and the 2-sweep
algorithm based on minimum-perimeter enclosing parallelogram achieve a approximation in this sweeping model.Comment: 9 pages, 4 figure
Notes on van der Meer Scan for Absolute Luminosity Measurement
An absolute luminosity can be measured in an accelerator by sweeping beams
transversely across each other in the so called van der Meer scan. We prove
that the method can be applied in the general case of arbitrary beam directions
and a separation scan plane. A simple method to develop an image of the beam in
its transverse plane from spatial distributions of interaction vertexes is also
proposed. From the beam images one can determine their overlap and the absolute
luminosity. This provides an alternative way of the luminosity measurement
during van der Meer scan.Comment: 1 figur
Volumes of solids swept tangentially around cylinders
In earlier work ([1]-[5]) the authors used the method of sweeping tangents to calculate area and arclength related to certain planar regions. This paper extends the method to determine volumes of solids. Specifically, take a region S in the upper half of the xy plane and allow the plane to sweep tangentially around a general cylinder with the x axis lying on the cylinder. The solid swept by S is called a solid tangent sweep. Its solid tangent cluster is the solid swept by S when the cylinder shrinks to the x axis. Theorem 1: The volume of the solid tangent sweep does not depend on the profile of the cylinder, so it is equal to the volume of the solid tangent cluster. The proof uses Mamikon's sweeping-tangent theorem: The area of a tangent sweep to a plane curve is equal to the area of its tangent cluster, together with a classical slicing principle: Two solids have equal volumes if their horizontal cross sections taken at any height have equal areas. Interesting families of tangentially swept solids of equal volume are constructed by varying the cylinder. For most families in this paper the solid tangent cluster is a classical solid of revolution whose volume is equal to that of each member of the family. We treat forty different examples including familiar solids such as pseudosphere, ellipsoid, paraboloid, hyperboloid, persoids, catenoid, and cardioid and strophoid of revolution, all of whose volumes are obtained with the extended method of sweeping tangents. Part II treats sweeping around more general surfaces
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