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 $n=1$ 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

Colonização micorrízica em Araucaria Angustifolia sob condições naturais : aspectos metodológicos e influência da comunidade vegetal

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