611 research outputs found
3D printing dimensional calibration shape: Clebsch Cubic
3D printing and other layer manufacturing processes are challenged by
dimensional accuracy. Several techniques are used to validate and calibrate
dimensional accuracy through the complete building envelope. The validation
process involves the growing and measuring of a shape with known parameters.
The measured result is compared with the intended digital model. Processes with
the risk of deformation after time or post processing may find this technique
beneficial. We propose to use objects from algebraic geometry as test shapes. A
cubic surface is given as the zero set of a 3rd degree polynomial with 3
variables. A class of cubics in real 3D space contains exactly 27 real lines.
We provide a library for the computer algebra system Singular which, from 6
given points in the plane, constructs a cubic and the lines on it. A surface
shape derived from a cubic offers simplicity to the dimensional comparison
process, in that the straight lines and many other features can be analytically
determined and easily measured using non-digital equipment. For example, the
surface contains so-called Eckardt points, in each of which three of the lines
intersect, and also other intersection points of pairs of lines. Distances
between these intersection points can easily be measured, since the points are
connected by straight lines. At all intersection points of lines, angles can be
verified. Hence, many features distributed over the build volume are known
analytically, and can be used for the validation process. Due to the thin shape
geometry the material required to produce an algebraic surface is minimal. This
paper is the first in a series that proposes the process chain to first define
a cubic with a configuration of lines in a given print volume and then to
develop the point cloud for the final manufacturing. Simple measuring
techniques are recommended.Comment: 8 pages, 1 figure, 1 tabl
Neumann-like integrable models
A countable class of integrable dynamical systems, with four dimensional
phase space and conserved quantities in involution (H\_n,I\_n) are exhibited.
For we recover Neumann sytem on T*S^2. All these systems are also
integrable at the quantum level.Comment: 8 pages; latex2e;no figure. To appear in Physics Letters
Triangular buckling patterns of twisted inextensible strips
When twisting a strip of paper or acetate under high longitudinal tension,
one observes, at some critical load, a buckling of the strip into a regular
triangular pattern. Very similar triangular facets have recently been observed
in solutions to a new set of geometrically-exact equations describing the
equilibrium shape of thin inextensible elastic strips. Here we formulate a
modified boundary-value problem for these equations and construct post-buckling
solutions in good agreement with the observed pattern in twisted strips. We
also study the force-extension and moment-twist behaviour of these strips by
varying the mode number n of triangular facets
Summer Climatic Gradients and Vegetation near Barrow, Alaska
Reports a June-Sept 1956 study of rainfall, evaporation evapotranspiration and vegetation at four sites: Nuwuk, the old Eskimo village site on the Pt Barrow spit, a beach ridge six mi SW of Nuwuk, a site near South Barrow test well no3, about 11 mi S of the beach ridge, and Meade River 28 mi from the ocean. Another site at Inaru River was used only for vegetation studies. Simple instruments gave periodic values for the three elements. Deviations of precipitation from US Weather Bureau records are tabulated. Distinctive changes in vegetation within a few miles with increase in shrubby and decrease in grassy components accompanied a general amelioration of climate inland. Sod block evapotranspirometers, weighed at intervals, showed more than a third increase in evapotranspiration rates between the ocean and 28 mi inland.Gradients du climat et de la végétation en été, près de Barrow, Alaska. À l'extrême pointe du nord de l'Alaska, on constate une amélioration générale du climat vers l'intérieur des terres, qui s'accompagne de changements visibles de la végétation en quelques milles seulement, dont une augmentation de l'élément broussailleux et une diminution d'importance de l'élément graminacé. Des instruments très simples ont permis de recueillir des données périodiques sur la pluie, l'évaporation et l'évapotranspiration. Le pesage à intervalles réguliers d'évapotranspiromètres à motte de gazon a donné des estimations raisonnables des taux d'évapotranspiration, qui augmentent de plus du tiers entre l'océan et des lieux situés à 28 milles (45 km) à l'intérieur
Clebsch (String) Parameterization of 3-Vectors and Their Actions
We discuss some properties of the intrinsically nonlinear Clebsch
decomposition of a vector field into three scalars in d=3. In particular, we
note and account for the incompleteness of this parameterization when
attempting to use it in variational principles involving Maxwell and
Chern-Simons actions. Similarities with string decomposition of metrics and
their actions are also pointed out.Comment: 4 pages, LaTeX; email correspondence to [email protected]
Crescimento micelial e germinação de esporos de patógenos de trigo em meios de cultura mais fungicidas 'in vitro'.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
Caracterização de raças de Pyrenophora tritici-repentis, agente etiológico da mancha amarela do trigo, no sul do Brasil.
bitstream/CNPT-2010/40333/1/p-bp60.pd
Ultrafast control of inelastic tunneling in a double semiconductor quantum
In a semiconductor-based double quantum well (QW) coupled to a degree of
freedom with an internal dynamics, we demonstrate that the electronic motion is
controllable within femtoseconds by applying appropriately shaped
electromagnetic pulses. In particular, we consider a pulse-driven AlxGa1-xAs
based symmetric double QW coupled to uniformly distributed or localized
vibrational modes and present analytical results for the lowest two levels.
These predictions are assessed and generalized by full-fledged numerical
simulations showing that localization and time-stabilization of the driven
electron dynamics is indeed possible under the conditions identified here, even
with a simultaneous excitations of vibrational modes.Comment: to be published in Appl.Phys.Let
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