Experimental analysis of influence of double-layer bump foils on aerodynamic thrust foil bearings performance

Purpose Gas thrust foil bearings (GTFBs) are used to balance the axial load of engines. However, in some working conditions of large axial force, such as the use of single impeller air compressor, the load capacity of GTFBs is still insufficient. To solve this problem, the load capacity can be improved by increasing the stiffness of bump foil. The purpose of this paper is to explore a scheme to effectively improve the performance of thrust foil bearings. In the paper, the stiffness of bump foil is improved by increasing the thickness of bump foil and using double-layer bump foil. Design/methodology/approach The foil deformation of GTFBs supported by three different types of bump foils, the relationship between friction power consumption and external force and the difference of limited load capacity were measured by experimental method. Findings The variation of the foil deformation, bearing stiffness, friction power consumption with the external force at different speeds and limited load capacity are obtained. Based on experimental results, the selection scheme of bump foil thickness is obtained. Originality/value This paper provides a feasible method for the performance optimization of GTFBs.

Anti-gravity technology by non-positive equivalent mass revealing UFO flying secrets

In this paper, a novel kind of anti-gravity technology by non-positive equivalent mass of aircraft is presented to try to reveal UFO flying secrets. Starting with a two-degree-of-freedom system, it is found that the system could produce an infinite acceleration under the condition of zero dynamic equivalent mass[1], and also provide a movement opposite to the direction of the external force under the negative equivalent mass[2]. These two cases with non-positive equivalent mass[3] could both be regarded as a novel kind of anti-gravity technology[4,5], which is also verified by a designed dynamic simulation experiment. For any aircraft that can be regarded as a multi-degree-of-freedom system driven by engine or other external forces[6], the non-positive equivalent mass could be designed out once the external input including gravity and engine exciting forces is known[7]. Thus the anti-gravity technology for any aircraft could be realized, which could also be extended to matters related to flight, such as space ships, missiles, airplanes, etc[8].

Superelasticity of a photo-actuating chiral salicylideneamine crystal

Superelasticity is a type of elastic response to an applied external force, caused by a phase transformation. Actuation of materials is also an elastic response to external stimuli such as light and heat. Although both superelasticity and actuation are deformations resulting from stimulus-induced stress, there is a phenomenological difference between the two with respect to whether force is an input or an output. Here, we report that a molecular crystal manifests superelasticity during photo-actuation under light irradiation. The crystal exhibits stepwise twisted actuation due to two effects, photoisomerization and photo-triggered phase transition, and the actuation behavior is simulated based on a dynamic multi-layer model. The simulation, in turn, reveals how the photoisomerization and phase transition progress in the crystal, indicating superelasticity induced by modest stress due to the formation of photoproducts. This work provides not only a successful simulation of stepwise twisted actuation, but also to the best of our knowledge the first indication of superelasticity induced by light.

Generalized periodic orbits of the time-periodically forced Kepler problem accumulating at the center and of circular and elliptic restricted three-body problems

In this paper, we consider a time-periodically forced Kepler problem in any dimension, with an external force which we only assume to be regular in a neighborhood of the attractive center. We prove that there exist infinitely many periodic orbits in this system, with possible double collisions with the center regularized, which accumulate at the attractive center. The result is obtained via a localization argument combined with a result on $$C^{1}$$ C 1 -persistence of closed orbits by a local homotopy-stretching argument. Consequently, by formulating the circular and elliptic restricted three-body problems of any dimension as time-periodically forced Kepler problems, we obtain that there exist infinitely many periodic orbits, with possible double collisions with the primaries regularized, accumulating at each of the primaries.

Effect of Scraper Geometry on Scraping HAP/ZrO2 Slurry in Digital Light Processing

Digital light processing (DLP) can be used to form HAP/ZrO2 mixed ceramic slurry. In the printing technology, the scraper geometry has an important effect on the scraping process; thus, it is necessary to conduct analysis. A modified lattice Boltzmann method (LBM) is proposed to conduct the numerical simulations according to the non-Newtonian behavior of the slurry. The Cross behavior of the slurry is viewed as a special external force; then, the traditional LBM including the true external force can be utilized effectively. The triangle, rectangle, trapezium, and rounded rectangle are the main considered section geometries of the scraper. When the flow velocity is set to 0.1 m/s, the results show that the maximum velocity occurs near the bottom surface of the scraper. In four situations, the velocity peak of the triangle case is 0.6270 m/s, which is the maximum, and much larger than the flow velocity of 0.1 m/s. The velocity peak of the rectangle case is 0.0466 m/s, which is the minimum. Although the velocity peak of the rounded rectangle case is 0.0556 m/s, the second velocity peak is 0.0465 m/s; the difference is smaller than that of the rectangle case. In addition, the streamlines figures show that the sharp corner leads to the obvious velocity change. In summary, the rounded rectangle is considered to be more suitable for scraping the HAP/ZrO2 mixed slurry.

Force Dependent Quantum Phase Transition in the Hybrid Optomechanical System

The optomechanics shows a great potential in quantum control and precise measurement due to appropriate mechanical control. Here we theoretically study the quantum phase transition in a hybrid atom-optomechanical cavity with an external force. Our study shows, in the thermodynamic limit, the critical value of quantum phase transition between the normal phase and super-radiant phase can be controlled and modified by the external force via the tunable frequency of optomechanics, then a force dependent quantum phase transition can be achieved in our system. Moreover, this force dependent quantum phase transition can be employed to detect the external force variation. In addition, our numerical simulations illustrate the sensitivity of the external force measurement can be improved by the squeezing properties of the quantum phase transition.

Acceleration of DNA Replication of Klenow Fragment by Small Resisting Force

DNA polymerases are an essential class of enzymes or molecular motors that catalyze processive DNA syntheses during DNA replications. A critical issue for DNA polymerases is their molecular mechanism of processive DNA replication. We have proposed a model for chemomechanical coupling of DNA polymerases before, based on which the predicted results have been provided about the dependence of DNA replication velocity upon the external force on Klenow fragment of DNA polymerase I. Here, we performed single molecule measurements of the replication velocity of Klenow fragment under the external force by using magnetic tweezers. The single molecule data verified quantitatively the previous theoretical predictions, which is critical to the chemomechanical coupling mechanism of DNA polymerases. A prominent characteristic for the Klenow fragment is that the replication velocity is independent of the assisting force whereas the velocity increases largely with the increase of the resisting force, attains the maximum velocity at about 3.8 pN and then decreases with the further increase of the resisting force.

Linear response theory in stock markets

Linear response theory relates the response of a system to a weak external force with its dynamics in equilibrium, subjected to fluctuations. Here, this framework is applied to financial markets; in particular we study the dynamics of a set of stocks from the NASDAQ during the last 20 years. Because unambiguous identification of external forces is not possible, critical events are identified in the series of stock prices as sudden changes, and the stock dynamics following an event is taken as the response to the external force. Linear response theory is applied with the log-return as the conjugate variable of the force, providing predictions for the average response of the price and return, which agree with observations, but fails to describe the volatility because this is expected to be beyond linear response. The identification of the conjugate variable allows us to define the perturbation energy for a system of stocks, and observe its relaxation after an event.