Characterizations of the $G_2(4)$ and $L_3(4)$ Near Octagons

A triple $(\mathcal{S},S,\mathcal{Q})$ consisting of a near polygon $\mathcal{S}$, a line spread $S$ of $\mathcal{S}$ and a set $\mathcal{Q}$ of quads of $\mathcal{S}$ is called a polygonal triple if certain nice properties are satisfied, among which there is the requirement that the point-line geometry $\mathcal{S}'$ formed by the lines of $S$ and the quads of $\mathcal{Q}$ is itself also a near polygon. This paper addresses the problem of classifying all near polygons $\mathcal{S}$ that admit a polygonal triple $(\mathcal{S},S,\mathcal{Q})$ for which a given generalized polygon $\mathcal{S}'$ is the associated near polygon. We obtain several nonexistence results and show that the $G_2(4)$ and $L_3(4)$ near octagons are the unique near octagons that admit polygonal triples whose quads are isomorphic to the generalized quadrangle $W(2)$ and whose associated near polygons are respectively isomorphic to the dual split Cayley hexagon $H^D(4)$ and the unique generalized hexagon of order $(4,1)$.

Kinematic Analysis and Verification of a New 5-DOF Parallel Mechanism

This paper first designs a new 5-DOF parallel mechanism with 5PUS-UPU, and then analyses its DOF by traditional Grubler–Kutzbach and motion spiral theory. It theoretically shows that the mechanism meets the requirement of five dimensions of freedoms including three-dimensional movement and two-dimensional rotation. Based on this, the real mechanism is built, but unfortunately it is found unstable in some positions. Grassmann line geometry method is applied to analyze its unstable problem caused by singular posture, and then an improving method is put forward to solve it. With the improved mechanism, closed loop vector method is employed to establish the inverse position equation of the parallel mechanism, and kinematics analysis is carried out to get the mapping relationships between position, speed, and acceleration of moving and fixed platform. Monte Carlo method is used to analyze the workspace of the mechanism, to explore the influencing factors of workspace, and then to get the better workspace. Finally, an experiment is designed to verify the mechanism working performance.

2.5D multifocusing imaging of crooked-line seismic surveys

Two-dimensional seismic surveys often are conducted along crooked line traverses due to the inaccessibility of rugged terrains, logistical and environmental restrictions, and budget limitations. The crookedness of line traverses, irregular topography, and complex subsurface geology with steeply dipping and curved interfaces could adversely affect the signal-to-noise ratio of the data. The crooked-line geometry violates the assumption of a straight-line survey that is a basic principle behind the 2D multifocusing (MF) method and leads to crossline spread of midpoints. Additionally, the crooked-line geometry can give rise to potential pitfalls and artifacts, thus, leads to difficulties in imaging and velocity-depth model estimation. We develop a novel multifocusing algorithm for crooked-line seismic data and revise the traveltime equation accordingly to achieve better signal alignment before stacking. Specifically, we present a 2.5D multifocusing reflection traveltime equation, which explicitly takes into account the midpoint dispersion and cross-dip effects. The new formulation corrects for normal, inline, and crossline dip moveouts simultaneously, which is significantly more accurate than removing these effects sequentially. Applying NMO, DMO, and CDMO separately tends to result in significant errors, especially for large offsets. The 2.5D multifocusing method can perform automatically with a coherence-based global optimization search on data. We investigated the accuracy of the new formulation by testing it on different synthetic models and a real seismic data set. Applying the proposed approach to the real data led to a high-resolution seismic image with a significant quality improvement compared to the conventional method. Numerical tests show that the new formula can accurately focus the primary reflections at their correct location, remove anomalous dip-dependent velocities, and extract true dips from seismic data for structural interpretation. The proposed method efficiently projects and extracts valuable 3D structural information when applied to crooked-line seismic surveys.

Magnetic dipole interaction with multipole magnetic field lines of neutron stars

Conservation of magnetic flux is associated with regions of the powerful magnetic fields (B ∽ 1013 G) near neutron stars' surface. The vector potential generated by moving electric charge Q is uniformly distributed within a Neutron star's surface (radius R). The evolution of the magnetic field of isolated neutron stars is studied and based on magnetic flux conservation; the multipolar magnetic fields for (l = 1; l = 2; l = 3; l = 4) have calculated. We developed the field line equations and simulated the magnetic field line geometry for the interaction between neutron stars’ dipole–multipolar magnetic fields using the MATLAB software program.

Coulomb collisions in strongly anisotropic plasmas II. Cyclotron cooling in laboratory pair plasmas

The behaviour of a strongly magnetised collisional electron–positron plasma that is optically thin to cyclotron radiation is considered, and the distribution functions accessible to it on the various timescales in the system are calculated. Particular attention is paid to the limit in which the collision time exceeds the radiation emission time, making the electron distribution function strongly anisotropic. Indeed, these are the exact conditions likely to be attained in the first laboratory electron–positron plasma experiments currently being developed, which will typically have very low densities and be confined in very strong magnetic fields. The constraint of strong magnetisation adds an additional complication in that long-range Coulomb collisions, which are usually negligible, must now be considered. A rigorous collision operator for these long-range collisions has never been written down. Nevertheless, we show that the collisional scattering can be accounted for without knowing the explicit form of this collision operator. The rate of radiation emission is calculated and it is found that the loss of energy from the plasma is proportional to the parallel collision frequency multiplied by a factor that only depends logarithmically on plasma parameters. That is, this is a self-accelerating process, meaning that the bulk of the energy will be lost in a few collision times. We show that in a simple case, that of straight field-line geometry, there are no unstable drift waves in such plasmas, despite being far from Maxwellian.

Study of a New 5-DOF Parallel Mechanism for Multi-Directional 3D Printing

This paper first designs a new 5-DOF parallel mechanism with 5PUS-UPU for multi-directional 3D printing, and then analyses its DOF by traditional Grubler-Kutzbach and motion spiral theory. It theoretically shows that the mechanism meets the requirement of 5 dimensions of freedoms including three-dimensional movement and two-dimensional rotation. Basing on this, the real mechanism is built, but unfortunately it is found unstable in some positions. Grassmann line geometry method is applied to analyze its unstable problem caused by singular posture, and then an improving method is put forward to solve it. With the improved mechanism, closed loop vector method is employed to establish the inverse position equation of the parallel mechanism, and kinematics analysis is carried out to get the mapping relationships between position, speed and acceleration of moving and fixed platform, Monte Carlo method is used to analyze the workspace of the mechanism, to explore the influencing factors of workspace, and then to get the better workspace. Finally an experiment is designed to verify the mechanism working performance to satisfy the spatial motion requirements of multi-directional 3D printing.

PEMBUATAN INFORMASI GEOSPASIAL SARANA DAN PRASARANA KELURAHAN WATES KABUPATEN KULON PROGO PADA SKALA 1:15.000

ABSTRAK Field Research Center (FRC) merupakan bagian dari program Teaching Industry Sekolah Vokasi Universitas Gadjah Mada. FRC dibangun bertujuan untuk mengembangkan hasil penelitian dan pengabdian agar menjadi sebuah produk yang dapat dimanfaatkan oleh masyarakat serta mendekatkan mahasiswa pada obyek materi pembelajaran agar menjadi lulusan yang siap bekerja. Rencana FRC akan dibangun di atas tanah seluas 6,5 hektar di Kelurahan Wates, Kabupaten Kulon Progo. Disekitar lokasi pembangunan FRC, terdiri atas kawasan penyangga seluas 29 hektar. Kawasan penyangganya terdiri atas berbagai berbagai sarana dan prasarana, seperti sarana pendidikan, kesehatan, pertahanan dan keamanan, jalan, sungai, rel kereta api, dan lain sebagainya. Penelitian ini bertujuan untuk menyajikan informasi geospasial sarana dan prasarana yang berada disekitar lokasi FRC. Data yang digunakan dalam penelitian ini terdiri atas data citra foto udara dan hasil dijitasi. Data citra foto udara diambil dengan menggunakan wahana pesawat tanpa awak (UAV) dengan tinggi terbang 270 meter dan ketelitian 0,775 pix. Data vektor yang dihasilkan dari proses dijitasi on-screen terdiri atas unsur geospasial bangunan (geometri poligon dan titik), jalan (geometri poligon), sungai (geometri poligon), drainase (geometri garis), rel kereta api (geometri garis), dan batas administrasi kelurahan (geometri garis). Masing-masing unsur geospasial disertai dengan data atribut yang diperoleh dari hasil survei lapangan. Sistem informasi geospasial sarana dan prasarana disajikan dalam skala 1:15.000. Sistem informasi geospasial ini diharapkan dapat membantu Kelurahan Wates dalam mengembangkan sarana prasarana yang terdapat pada sekitar lokasi FRC. Kata Kunci: Field Research Center, sistem informasi geospasial, sarana prasarana, peta skala besarABSTRACT Field Research Center (FRC) is part of Teaching Industry program of Vocational School. FRC was build to develop research and service result into products. The products utilized by the community and bring students closer to learning material objects in order to become graduates who are ready to work. FRC will be build on 6.5 hectares of land in Kelurahan Wates, Kulon Progo Regency. Around the location of the FRC construction consists of a 29 hectare supporting area. The supporting area consists of various facilities and infrastructure, such as education, health, defense and security facilities, roads, rivers, railroads, and so on. This study aims to present geospatial information for infrastructure around the FRC location. The data used in this study consisted of aerial photo image data and results of digitization. Aerial photo image data taken using a drone vehicle (UAV) with a height of 270 meters and accuracy of 0.775 pix. Vector data generated from digitizing on-screen process. These are consists of six geospatial elements, such as building (polygon geometry and dots), roads (polygon geometry), rivers (polygon geometry), drainage (line geometry), railroad tracks (line geometry), and boundaries village administration (line geometry). Each geospatial element accompanied by attribute data that obtained from field surveys. Geospatial information about infrastructure presented on big scale of 1: 15,000. This geospatial information expected to help Kelurahan Wates developing infrastructure around the FRC location. Keywords: Field Research Center, geospatial information system, infrastructures, big scale map

Surface textures suppress viscoelastic braking on soft substrates

A gravity-driven droplet will rapidly flow down an inclined substrate, resisted only by stresses inside the liquid. If the substrate is compliant, with an elastic modulusG< 100 kPa, the droplet will markedly slow as a consequence of viscoelastic braking. This phenomenon arises due to deformations of the solid at the moving contact line, enhancing dissipation in the solid phase. Here, we pattern compliant surfaces with textures and probe their interaction with droplets. We show that the superhydrophobic Cassie state, where a droplet is supported atop air-immersed textures, is preserved on soft textured substrates. Confocal microscopy reveals that every texture in contact with the liquid is deformed by capillary stresses. This deformation is coupled to liquid pinning induced by the orientation of contact lines atop soft textures. Thus, compared to flat substrates, greater forcing is required for the onset of drop motion when the soft solid is textured. Surprisingly, droplet velocities down inclined soft or hard textured substrates are indistinguishable; the textures thus suppress viscoelastic braking despite substantial fluid–solid contact. High-speed microscopy shows that contact line velocities atop the pillars vastly exceed those associated with viscoelastic braking. This velocity regime involves less deformation, thus less dissipation, in the solid phase. Such rapid motions are only possible because the textures introduce a new scale and contact-line geometry. The contact-line orientation atop soft pillars induces significant deflections of the pillars on the receding edge of the droplet; calculations confirm that this does not slow down the droplet.