Mechanical induction of oscillatory movement in demembranated, immotile flagella of sea urchin sperm at very low ATP concentrations

ABSTRACTOscillation is a characteristic feature of eukaryotic flagellar movement. The mechanism involves the control of dynein-driven microtubule sliding under self-regulatory mechanical feedback within the axoneme. To define the essential factors determining the induction of oscillation, we developed a novel experiment by applying mechanical deformation of demembranated, immotile sea urchin sperm flagella at very low ATP concentrations, below the threshold of ATP required for spontaneous beating. Upon application of mechanical deformation at above 1.5 µmol l−1 ATP, a pair of bends could be induced and was accompanied by bend growth and propagation, followed by switching the bending direction. For an oscillatory, cyclical bending response to occur, the velocity of bend propagation towards the flagellar tip must be kept above certain levels. Continuous formation of new bends at the flagellar base was coupled with synchronized decay of the preceding paired bends. Induction of cyclical bends was initiated in a constant direction relative to the axis of the flagellar 9+2 structure, and resulted in the so-called principal bend. In addition, stoppage of the bending response occasionally occurred during development of a new principal bend, and in this situation, formation of a new reverse bend did not occur. This observation indicates that the reverse bend is always active, opposing the principal bend. The results show that mechanical strain of bending is a central component regulating the bend oscillation, and switching of the bend direction appears to be controlled, in part, by the velocity of wave propagation.

Plio-Quaternary tectonic evolution of the southern margin of the Alboran Basin (Western Mediterranean)

Progress in the understanding and dating of the sedimentary record of the Alboran Basin allows us to propose a model of its tectonic evolution since the Pliocene. After a period of extension, the Alboran Basin underwent a progressive tectonic inversion starting around 9–7.5 Ma. The Alboran Ridge is a NE–SW transpressive structure accommodating the shortening in the basin. We mapped its southwestern termination, a Pliocene rhombic structure exhibiting series of folds and thrusts. The active Al-Idrissi Fault zone (AIF) is a Pleistocene strike-slip structure trending NNE–SSW. The AIF crosses the Alboran Ridge and connects to the transtensive Nekor Basin and the Nekor Fault to the south. In the Moroccan shelf and at the edge of a submerged volcano we dated the inception of the local subsidence at 1.81–1.12 Ma. The subsidence marks the propagation of the AIF toward the Nekor Basin. Pliocene thrusts and folds and Quaternary transtension appear at first sight to act at different tectonic periods but reflect the long-term evolution of a transpressive system. Despite the constant direction of Africa–Eurasia convergence since 6 Ma, along the southern margin of the Alboran Basin, the Pliocene–Quaternary compression evolves from transpressive to transtensive along the AIF and the Nekor Basin. This system reflects the logical evolution of the deformation of the Alboran Basin under the indentation of the African lithosphere.

Ground Mobile Bricard Mechanism

A novel application of the well-known single degree-of-freedom (DOF) Bricard mechanism is proposed in this paper. By optimizing the links’ shape and installing motors reasonably, we put forward a ground mobile Bricard mechanism that can move in a constant direction and change its moving direction by using its singular position. The types of kowtowing and spinning modes (dual-mode) are carried out, and the gaits are planned. Finally, the motion simulation and prototype experiment testify that the analyses are correct and the idea of the dual-mode ground mobile Bricard mechanism is feasible.

The slant helices according to N-Bishop frame of the spacelike curve with spacelike principal normal in Minkowski 3-space

If the principal normal vector field of a curve makes a constant angle with constant direction, this curve is called as slant helix. In this paper, a slant helix is defined according to N-Bishop frame of the spacelike curve with a spacelike principal normal. Some characterizations of the slant helices are obtained according to spacelike curve N-Bishop frame with a spacelike principal normal, benefiting from the definition of the slant helices.

Plio-Quaternary tectonic evolution of the southern margin of the Alboran Basin (Western Mediterranean)

Progresses in understanding the sedimentary dynamic of the Western Alboran Basin lead us to propose a model of evolution of its tectonic inversion since the Pliocene to present-time. Extensive and strike-slip structures accommodate the Miocene back-arc extension of the Alboran Basin, but undergo progressive tectonic inversion since the Tortonian. Across the Alboran Basin, the Alboran Ridge becomes a transpressive structure accommodating the shortening. We map its southwestern termination: a Pliocene rhombic structure exhibiting series of folds and thrusts. A younger structure, the Al-Idrissi fault zone (AIF), is Pleistocene to present-day active strike-slip fault zone. This fault zone crosses the Alboran Ridge and connects southward to the transtensive Nekor Basin and the Nekor fault. In the Moroccan shelf and at the edge of a submerged volcano, we date the inception of the local shelf subsidence from the 1.81–1.12 Ma. It marks the propagation of the AIF toward the Nekor Basin. Pliocene thrusts and folds and Quaternary transtension appear at first sight as different tectonic periods but reflects the long-term evolution of a transpressive system. Despite a constant direction of Africa/Eurasia convergence since 5 Ma at the scale of the southern margin of Alboran Basin, the Pliocene-Quaternary inversion evolves from transpressive to transtensive on the AIF and the Nekor Basin. This system reflects the expected evolution of the deformation of the Alboran Basin under the indentation of the African lithosphere.

Ground mobile Bennett mechanism

This paper presents a novel application of the well-known single degree of freedom Bennett mechanism. By optimizing the link’s shape and the weight distribution of the Bennett mechanism, we put forward a ground mobile mechanism that can move in a constant direction and change its moving direction with only one actuator. A type of tumbling gait is proposed and kinematic and dynamic analyses of the gait are carried out. Finally, a series of experiments are performed on a manufactured prototype. The results verify the tumbling gait and functionality of the mobile mechanism.

New classification results on surfaces with a canonical principal direction in the Minkowski 3-space

In this paper, wecharacterize and classify all surfaces endowed with canonical principal direction relative to a space-like and light-like, constant direction in the Minkowski 3-space.

Ground Mobile Schatz Mechanism

We put forward a novel proposition that a mechanism can move in a constant direction and change its moving directions only by one actuator and construct a single-DOF (degree of freedom) ground mobile mechanism based on the well-known Schatz mechanism. This ground mobile Schatz mechanism has six links, one of which is designed as a spoke octahedron and an other one as a tail link. When the actuator rotates in one direction, the spoke octahedron can roll on the ground to let the ground mobile Schatz mechanism to move in a straight line pushed by the tail link. When the actuator rotates in the opposite direction, the tail link can be lifted to change its landing point and the relative position between it and the spoke octahedron, then the spoke octahedron can roll in another direction pushed by the tail link. In addition, it is also an untraditional application of the Schatz mechanism that it is used as a novel ground mobile mechanism. Locomotion analysis, gait planning and stability analysis are performed, respectively, and a prototype is developed and tested.

Design of a Four-Station Translational and Rotary Worktable for Special Occasions

A newly developed four-station translational and rotary worktable can be applied for complex human-machine hybrid operations and dangerous heat treatment operations. And the design can guarantee closed operations without involvement of human when the worktable rotates to the concentrated area, while the installation or other manual processing when the worktable rotates to the separate area. In addition, by designing innovative rotating and track-changing mechanism and the direction-holding mechanism, the work piece remains the constant direction in the rotation process. Furthermore, the interference problem of the Geneva mechanism of the track-changing fork is analyzed. Consequently, the smaller the angle of fork notch is, the smaller the force that fork reacts on the support shaft is, meanwhile, the strength can be satisfied more easily. The optimal angle of Y-fork is 90 degree. The application of the four-station translational and rotary worktable can achieve multi-step continuous process, save workspace and improve production efficiency.