Twisted Surface Research Articles

Megahertz-range longitudinal guided wave excitation by a flexible magnetostrictive sensor for steel strand inspection

A new type of sensing coil for magnetostrictive sensor (MsS) is presented in this paper. The flexible printed meander coil (FPMC) can offer micron level dimensional accuracy for the structure parameters which link to the central frequency of the MsS. Thus, the actual central frequency of the FPMC-based MsS can precisely meet the expected value. The number of coil groups in the FPMC is optimised to maximise the excited and received energy of the megahertz-range longitudinal guided waves in the strand and its central rod. Meanwhile, the FPMC can be easily wrapped onto the twisted strand surface and also can be installed onto the central rod of the strand after being wrapped into multiple layers. With the proposed megahertz-range FPMC-based MsS, the rod/strand inspection system is potential to be applied for practical inspections, having higher axial inspection resolution and sensitivity to small defects.

Discussion on Several Problems of Designing Steel Tubular Joints

This paper investigated some problems in steel tubuar joints design.The joint stiffness has played an important role in evaluating the whole stability of the structure. Currently there is no clear standard for judging joint stiffness, this paper presents a way to identify the steel joints stiffness. Accordingly, the analysis results of joint stiffness can be directly applied to practical engineering. This paper also proposed new steel welded joints which adapt to space slant and twisted surface for solving problem about square steel pipe joints design. This joints not only ensure regional stiffness and have an attractive appearance, simple structure, but also apply to engineering very well. The result of the research has a certain value to practical engineering design.

Del Pezzo surfaces of degree 4 and their relation to Kummer surfaces

In this note, which has little pretence to originality, we clarify the relation between the geometry of del Pezzo surfaces of degree 4 and their realization as the zero set of two quadratic forms in five variables. We also review the classical description of the desingularized Kummer surface K constructed from the Jacobian J of a curve C of genus 2 as the zero set of three quadratic forms in six variables (Plucker, Kummer, Klein [7], [6], see [5] or [3] for a modern treatment). If C has a rational Weierstrass point, a partial diagonalization of this system gives rise to a natural projection onto a hyperplane, defining a finite morphism π : K → X of degree 2 onto a del Pezzo surface X of degree 4 (see [9, §6]). We show that X is the blow-up of Pk in the images of the five other Weierstrass points of C under the embedding of Pk as a conic in Pk. The morphism π sends the 16 lines on K to the 16 lines on X, and is equivariant with respect to the action of the subgroup of 2-division points J [2] ⊂ J . Thus π gives rise to a morphism from the twisted Kummer surface to the twisted del Pezzo surface. In our presentation it is obvious that all del Pezzo surfaces of degree 4 can be obtained in this way, an observation made by Victor Flynn in [4]. The fact that any 2-covering of J maps to a del Pezzo surface of degree 4 was first observed in [2], and used in [2], [1] and [9] to construct and visualize elements of order 2 in the Tate–Shafarevich group of J over Q using the theory of the Brauer– Manin obstruction on del Pezzo surfaces of degree 4. It was the author’s desire to understand the geometry behind these calculations that prompted him to write this note. I would like to thank Igor Dolgachev for useful discussions.

Two-color surface lattice solitons

We study the properties of surface solitons generated at the edge of a semi-infinite photonic lattice in nonlinear quadratic media, namely two-color surface lattice solitons. We analyze the impact of phase mismatch on the existence and stability of nonlinear surface modes and find novel classes of two-color twisted surface solitons, which are stable in a large domain of their existence.

Experimental study of current sheet evolution in magnetic configurations with null-points and X-lines

A review is presented on experimental research of current sheet formation in 3D magnetic configurations containing null-points and/or singular lines of the X-type. Formation of current sheets is revealed to occur in various 3D configurations, both with and without isolated magnetic null-points, specifically in configurations with X-lines. Local characteristics of 3D magnetic configuration define the parameters of the current sheet, which forms usually a twisted surface with an angular orientation determined by a local value of the transverse magnetic field gradient. A degree of plasma compression into the sheet decreases with a rise of longitudinal magnetic field component, displaying a transition to a behavior of uncompressible plasma. It is established that current sheet formation and magnetic reconnection processes can take place within a limited range of initial conditions, while a gradient of transverse magnetic field is the most important parameter.

Ribosomal protein L5 has a highly twisted concave surface and flexible arms responsible for rRNA binding.

Ribosomal protein L5 is a 5S rRNA binding protein in the large subunit and plays an essential role in the promotion of a particular conformation of 5S rRNA. The crystal structure of the ribosomal protein L5 from Bacillus stearothermophilus has been determined at 1.8 A resolution. The molecule consists of a five-stranded antiparallel beta-sheet and four alpha-helices, which fold in a way that is topologically similar to the ribonucleoprotein (RNP) domain. The molecular shape and electrostatic representation suggest that the concave surface and loop regions are involved in 5S rRNA binding. To identify amino acid residues responsible for 5S rRNA binding, we made use of Ala-scanning mutagenesis of evolutionarily conserved amino acids occurring in the beta-strands and loop regions. The mutations of Asn37 at the beta1-strand and Gln63 at the loop between helix 2 and beta3-strand as well as that of Phe77 at the tip of the loop structure between the beta2- and beta3-strands caused a significant reduction in 5S rRNA binding. In addition, the mutations of Thr90 on the beta3-strand and Ile141 and Asp144 at the loop between beta4- and beta5-strands moderately reduced the 5S rRNA-binding affinity. Comparison of these results with the more recently analyzed structure of the 50S subunit from Haloarcula marismortui suggests that there are significant differences in the structure at N- and C-terminal regions and probably in the 5S rRNA binding.

A tight polyhedral immersion of the twisted surface of Euler characteristic −3

Early studies of tight surfaces showed that almost every surface can be immersed tightly in three-space. For these surfaces we can ask: How many significantly different tight immersions are there? If we consider two such immersions to be the same when they are image homotopic, then we can answer the question by determining the number of homotopy classes where tight immersions are possible. A complete description of all classes of immersions under image homotopy already exists, and tight examples are known in all but three of the classes where tight immersions are possible. In this paper we produce examples in two of those three missing classes, and conjecture that no tight immersion exists in the third.

Constraints on arm position when pointing in three dimensions: Donders' law and the Fick gimbal strategy.

1. While making saccades between targets with the head stationary, eye positions are constrained to two of the possible three degrees of freedom. Classically this constraint has been described by Donders' and Listing's laws. The objective was to determine whether these laws also apply for the straight arm when pointing between different targets. Thus we determined whether the arm adopts only one angular position for every pointing direction (Donders' law) and whether these positions can be described by rotations from a reference position about axes that lie in a plane (Listing's law). 2. The angular positions (orientations) of the arm in three-dimensional space were studied as subjects pointed with a straight arm at different targets. Arm position was measured with the search coil technique by means of coils attached to the back of the hand. Pointing was studied over a range of +/- 45 degrees in all directions from a central target located 45 degrees to the right of the straight-ahead position. 3. The positions of the arm in space were described by quaternion vectors, i.e., a particular position was described in terms of the axis and amplitude of a rotation from a reference position to that position. Using this description, it was found that the straight arm adopted a similar orientation (standard deviations ranged from 2.8 to 4.8 degrees) when pointing at a particular target irrespective of which target from which it had moved. 4. The angular position vectors for arm positions associated with relatively small movements (e.g., less than +/- 30 degrees) lay in a flat surface with minimal torsion. At first sight, this surface appeared to be similar to Listing's plane of the eye. However, for positions associated with larger movements (e.g., +/- 45 degrees) it became apparent that, unlike the eye, the surface deviated from one obeying Listing's law, i.e., it was twisted and showed torsion like that produced by rotations around the horizontal and vertical axes of a Fick gimbal. (The characteristic of a Fick gimbal is that the vertical axis is fixed, whereas the horizontal axis moves with the gimbal.) 5. Although there were differences between subjects, all showed a twisted position vector surface. The twist was always in the same direction, and it was always less than that of a Fick gimbal. 6. This position vector surface had a similar shape whether the arm was stationary or was moving between targets, whether subjects pointed with or without vision, and whether the pointing arm had moved between targets or from a bent-elbow position on the lap.(ABSTRACT TRUNCATED AT 400 WORDS)

Contacts between the LexA repressor--or its DNA-binding domain--and the backbone of the recA operator DNA.

Using hydroxyl radical footprinting and ethylation interference experiments, we have determined the backbone contacts made by the entire LexA repressor and its amino-terminal fragment with the recA operator DNA. These techniques reveal essentially the same contacts between both proteins and one side of the DNA helix if one assumes that the DNA stays in the normal B-conformation. This result is somewhat unexpected because protection of guanine bases against methylation suggested a somewhat twisted recognition surface. The backbone contacts revealed by both methods are symmetrically disposed with respect to the center of the operator, providing further evidence that the operator binds two LexA monomers. Each half-operator contains seven interfering phosphates. These phosphates are found on both sides of the 5'-CTGT sequence that is believed to be the principal recognition target. On the side close to the center of the operator are found two phosphates, whereas the other five are clustered on the side apart from the dyad axis. We are not aware of such an extended cluster of interfering phosphates for any other DNA-binding protein. A quantification of the hydroxyl radical footprints allowed us to compare further the affinity of the LexA repressor for the recA operator with that of its isolated DNA binding domain. We find an only 13-fold higher binding constant for LexA than for its amino-terminal domain, which is in good agreement with our earlier results for the uvrA operator using a completely different binding assay.