Nature’s Perfection: Aristotle and Descartes on Motion and Purpose

Descartes holds that, insofar as nature is a purposeless, unthinking, extended substance, there could be no final causes in physics. Descartes’ derivation of his three laws of motion from the perfections of God thus underwrites a rejection of Aristotle’s conception of natural self-motion and teleology. Aristotle derived his conception of the purposeful action of sublunar creatures from his notion that superlunar bodies are perfect, eternal, living beings, via the thesis that circular motion is more complete or perfect than rectilinear motion. Descartes’ reduction of circular motion to rectilinear motion, achieved through his theological foundation of the laws of motion, thus marks a crucial break from Aristotle’s philosophy of nature. This paper argues that the shift from the Aristotelian conception of nature as self-moving and teleological to the Cartesian conception of nature as purposeless and inert, is not an empirical discovery but is rooted in differing conceptions of where perfection lies in nature.

Two improved scanning path planning algorithms and a 3D printing control system with circular motion controller

Purpose This paper aims to improve the infilling efficiency and the quality of parts forming. It proposes two improved scanning path planning algorithm based on velocity orthogonal decomposition. Design/methodology/approach The algorithms this paper proposes replace empty paths and corners with circular segments, driving each axis synchronously according to the SIN or COS velocity curve to make the extruder always moves at a constant speed at maximum during the infilling process. Also, to support the improved algorithms, a three-dimensional (3D) printing control system based on circular motion controller is also designed. Findings The simulation and experiment results show that the improved algorithms are effective, and the printing time is shortened more significantly, especially in the case of small or complex models. What’s more, the optimized algorithm is not only compact in shape but also not obvious in edge warping. Research limitations/implications The algorithms in this paper are not applicable to traditional motion controllers. Practical implications The algorithms in this paper improve the infilling efficiency and the quality of parts forming. Social implications There are no social implications in this paper. Originality/value The specific optimization method of parallel-line scanning algorithm based on velocity orthogonal decomposition is replacing the empty paths with arc corners. And the specific optimization method of contour offsetting algorithm based on velocity orthogonal decomposition is to add connection paths between adjacent contours and turn all straight corners into arcs. What’s more, the 3D printing control system based on the circular motion controller can achieve multi-axis parallel motion to support these two improved path scanning algorithms.

Astrometric observations of water maser sources toward the Galactic Center with VLBI

The Central Molecular Zone (CMZ) in the Galactic Center region shows outstanding non-circular motion unlike the Galactic disk. Although several models describing this non-circular motion are proposed, an uniform kinematic model of the CMZ orbit is not appeared. Three dimensional velocity information including proper motions will be critical to constrain the orbital models of the CMZ because most of models proposed are devised to reproduce the line-of-sight velocity pro les of the molecular clouds in this region. To reveal the dynamics of the Galactic center region, we conducted VLBI astrometric observations of 22 GHz water maser sources toward the Galactic center with VERA. By measuring parallaxes and proper motions, we can identify whether each source is actually located in the CMZ or not, and identify the three dimensional positions and velocities in the non-circular orbit if the source is located in the CMZ. We show the results of astrometric study for several maser sources associated with molecular clouds toward the Galactic center including Sgr B2 complex and Sgr D HII region. The parallax measurement toward Sgr B2 obtained the parallax of 0.133 0:038 mas, and its proper motions indicated that Sgr B2 complex is moving toward the positive Galactic longitude with V = 100 km s−1 relative to Sgr A*.

Plagued by confusion

A response to Nick England’s letter “Going in circles” and Alan Calverd’s and Tim Watson’s letters “Weighty issue” concerning the common misunderstandings about circular motion and weight.

Coleridge’s Imperfect Circles

<p>This thesis takes as its starting point Coleridge’s assertion that “[t]he common end of all . . . Poems is . . . to make those events which in real or imagined History move in a strait [sic] Line, assume to our Understandings a circular motion” (CL 4: 545). Coleridge’s so-called “Conversation” poems seem to conform most conspicuously to this aesthetic theory, structured as they are to return to their starting points at their conclusions. The assumption, however, that this comforting circular structure is commensurate with the sense of these poems can be questioned, for the conclusions of the “Conversation” poems are rarely, if ever, reassuring. The formal circularity of these poems is frequently achieved more by persuasive rhetoric than by any cohesion of elements. The circular structure encourages the reader’s expectations of unity and synthesis, but ultimately these expectations are disappointed, and instead the reader is surprised by an ending more troubling than the rhetoric of return and reassurance would suggest. Taking three “Conversation” poems as case studies (“The Eolian Harp,” “This Lime-Tree Bower My Prison,” and “Frost at Midnight”), this thesis attempts to explicate those tensions which exist in the “Conversation” poems between form and effect, between structure and sense.</p>

Coleridge’s Imperfect Circles

<p>This thesis takes as its starting point Coleridge’s assertion that “[t]he common end of all . . . Poems is . . . to make those events which in real or imagined History move in a strait [sic] Line, assume to our Understandings a circular motion” (CL 4: 545). Coleridge’s so-called “Conversation” poems seem to conform most conspicuously to this aesthetic theory, structured as they are to return to their starting points at their conclusions. The assumption, however, that this comforting circular structure is commensurate with the sense of these poems can be questioned, for the conclusions of the “Conversation” poems are rarely, if ever, reassuring. The formal circularity of these poems is frequently achieved more by persuasive rhetoric than by any cohesion of elements. The circular structure encourages the reader’s expectations of unity and synthesis, but ultimately these expectations are disappointed, and instead the reader is surprised by an ending more troubling than the rhetoric of return and reassurance would suggest. Taking three “Conversation” poems as case studies (“The Eolian Harp,” “This Lime-Tree Bower My Prison,” and “Frost at Midnight”), this thesis attempts to explicate those tensions which exist in the “Conversation” poems between form and effect, between structure and sense.</p>

Schwarzschild–Droste solution

The spherically symmetric vacuum solution to the Einstein field equation (Schwarzschild-Droste solution) is derived and associated physical phenomena derived and explained. It is shown how to obtain the Christoffel symbols by the Euler-Lagrange method, and hence the metric for the general spherically symmetric vacuum. Equations for general orbits are presented, and their solution for radial motion and for circular motion. Geodetic (de Sitter) precession is calculated exactly for circular orbits. The null geodesics (photon worldlines) are obtained, and the gravitational redshift. Emission from an accretion disc is calculated.

The application of smartphone sensors to promote cognitive abilities easier and more effective physics learning

The use of sensor on smartphones as physics learning media encourages teachers to reconstruct teaching methods. This paper presents the effect on students’ cognitive abilities using an accelerometer and a gyroscope sensor simultaneously in learning circular motion, as well as students’ responses and the effectiveness of sensor media on smartphones used. A pre-experimental research design was used in this study which involved 12 students of XII MIPA at SMA Negeri 1 Pagaden Subang Jawa Barat. They learned circular motion guided by the smartphone sensors-based worksheets and were tested using an essay test for cognitive abilities measurements. Meanwhile, students’ responses and the effectiveness were obtained using a Likert scale questionnaire. The improvement of students’ cognitive abilities was significantly higher than the pretest which was obtained from the N-gain with a final value of 0.41. Worksheets using smartphone sensor media were more effective than conventional learning. In addition, students showed a positive response in which 93.75% of students were interested, 85,42% were motivated to learn the circular motion, and 91.14% of students became easier in understanding physics concepts.