Instability Mode and Movement Characteristics of Dangerous Rock Body in Steep Rock Slope

The cutting relationship and development degree of structural plane control the instability mode and scale of rock slope. The trajectory of rock mass after instability is an important basis for the design of dangerous rock prevention. The back slope of a residential area was investigated in this paper. Based on the survey data of the field structure surfaces, the possible instability mode of the slope rock mass was analyzed by using the stereographic projection method. The shear strength parameters of the rock mass were inverted through the investigation of dangerous rock mass. Finally, ANSYS/LS-DYNA was used to simulate the dangerous rock mass motion trajectory. This study provides a reference for the analysis of the instability process of single rock.

The Use of a Single Trunk-Mounted Accelerometer to Detect Changes in Center of Mass Motion Linked to Lower-Leg Overuse Injuries: A Prospective Study

Movement dynamics during running was previously characterized using a trunk-mounted accelerometer, and were associated with a history of overuse injuries. However, it remains unknown if these measures are also linked to the development of overuse injuries. The aim of this study was therefore to determine how movement dynamics alter in response to fatigue, and the possible link with developing lower-leg overuse injuries during a six-month follow-up period. Two hundred and eight movement science university students completed a 12-min all-out run while wearing a trunk-mounted accelerometer. Dynamic stability, dynamic loading and spatiotemporal measures were extracted from the accelerometer. Participants sustaining an injury within the 6-month period demonstrated significantly higher RMS ratio values in the vertical direction and lower RMS ratio values in the anteroposterior direction, and lower impact acceleration values in the anteroposterior direction in an unfatigued state compared to the uninjured group. They also demonstrated an increase in dynamic loading in the horizontal plane during the run. In addition, with running fatigue both groups exhibited changes in dynamic stability and loading measures. These results show the potential of using a single trunk-mounted accelerometer to detect changes in movement dynamics that are linked to lower-leg overuse injuries.

Mode-Dependent Selective Detection of Humidity and Helium Using Electromagnetically Actuated Clamped Guided MEMS Resonators

In this work, we demonstrate a selective gas sensor based on monitoring two different detection mechanisms; absorption and thermal conductivity. To illustrate the concept, we utilize a resonator composed of a clamped-guided arch beam connected to flexural beams and a T-shaped moveable mass. The resonator has two distinct out-of-plane modes in which the mass motion dominates the first mode while the motion of the flexural beam dominates the second mode. A highly disperse graphene oxide (GO) solution is prepared and drop-casted over the moveable mass structure using the inkjet printer for humidity sensing. On the other hand, the He is detected using the hot flexural beams. The results show no significant effect of humidity on the flexural mode (FM) nor for He on the mass mode (MM). This indicates a new technique for selectivity and identification. The device shows good sensitivity (50.1% to 50% RH @ MM and 39.2% to 50% He @ FM: (Vac = 1.5V)), linearity, and repeatability with excellent selectivity. It is demonstrated that the FM has great potential for detecting and categorizing different gases according to their thermal conductivity. The demonstrated multimode MEMS resonator can be a promising approach for the development of smart, highly selective, and sensitive gas/chemical sensors.

Noether’s theorem in statistical mechanics

Noether’s calculus of invariant variations yields exact identities from functional symmetries. The standard application to an action integral allows to identify conservation laws. Here we rather consider generating functionals, such as the free energy and the power functional, for equilibrium and driven many-body systems. Translational and rotational symmetry operations yield mechanical laws. These global identities express vanishing of total internal and total external forces and torques. We show that functional differentiation then leads to hierarchies of local sum rules that interrelate density correlators as well as static and time direct correlation functions, including memory. For anisotropic particles, orbital and spin motion become systematically coupled. The theory allows us to shed new light on the spatio-temporal coupling of correlations in complex systems. As applications we consider active Brownian particles, where the theory clarifies the role of interfacial forces in motility-induced phase separation. For active sedimentation, the center-of-mass motion is constrained by an internal Noether sum rule.

Distortion of a polycrystalline Al bar in a vice fixture: molecular dynamics analysis of grain movement and rotation

The deformation of a nano-sized polycrystalline Al bar under the action of vice plates is studied using molecular dynamics simulation. Two grain sizes are considered, fine-grained and coarse-grained. Deformation in the fine-grained sample is mainly caused by grain-boundary processes which induce grain displacement and rotation. Deformation in the coarse-grained sample is caused by grain-boundary processes and dislocation plasticity. The sample distortion manifests itself by the center-of-mass motion of the grains. Grain rotation is responsible for surface roughening after the loading process. While the plastic deformation is caused by the loading process, grain rearrangements under load release also contribute considerably to the final sample distortion.

Variable mass motion in the Hénon–Heiles system

In this work, we analyze the motion properties of the test particle, that has a variable mass within the frame of Hénon–Heiles system. We derive the equations of motion of the test particle which varies its mass according to Jean’s law. We also determine the quasi-Jacobi integral which shows the effective variation due to variable mass parameters. Further, we studied the locations of stationary points and their stability, after using Meshcherskii spacetime inverse transformations.

Modeling and validation of crankshaft speed fluctuations of a single-cylinder four-stroke diesel engine

In this study, a dynamic model of a single-cylinder four-stroke diesel engine has been created, and the crankshaft speed fluctuations have been simulated and validated. The dynamic model of the engine consists of the motion equations of the piston, conrod, and crankshaft. Conrod motion was modeled by two translational and one angular motion equations, by considering the kinetic energy resulted from the mass moment of inertia and conrod mass. Motion equations involve in-cylinder gas pressure forces, hydrodynamic and dry friction, mass inertia moments of moving parts, starter moment, and external load moment. The In-cylinder pressure profile used in the model was obtained experimentally to increase the accuracy of the model. Pressure profiles were expressed mathematically using the Fourier series. The motion equations were solved by using the Taylor series method. The solution of the mathematical model was performed by coding in the MATLAB interface. Cyclic speed fluctuations obtained from the model were compared with experimental results and found compitable. A validated model was used to analyze the effects of in-cylinder pressure, mass moment of inertia of crankshaft and connecting rod, friction, and piston mass. In experiments for 1500, 1800, 2400, and 2700 rpm engine speeds, crankshaft speed fluctuations were observed as 12.84%, 8.04%, 5.02%, and 4.44%, respectively. In simulations performed for the same speeds, crankshaft speed fluctuations were calculated as 10.45%, 7.56%, 4.49%, and 3.65%. Besides, it was observed that the speed fluctuations decreased as the average crankshaft speed value increased. In the simulation for 157.07, 188.49, 219.91, 251.32, and 282.74 rad/s crankshaft speeds, crankshaft speed fluctuations occurred at rates of 10.45%, 7.56%, 5.84%, 4.49%, and 3.65%, respectively. The effective engine power was achieved as 5.25 kW at an average crankshaft angular speed of 219.91 rad/s. The power of friction loss in the engine was determined as 0.68 kW.

Approaching the motional ground state of a 10-kg object

The motion of a mechanical object, even a human-sized object, should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult because the thermal environment masks any quantum signature of the object’s motion. The thermal environment also masks the effects of proposed modifications of quantum mechanics at large mass scales. We prepared the center-of-mass motion of a 10-kilogram mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nanokelvin, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. Our approach will enable the possibility of probing gravity on massive quantum systems.

Distortion of a poly-crystalline Al bar in a vice fixture: Molecular dynamics analysis of grain movement and rotation

The deformation of a nano-sized polycrystalline Al bar under the action of vice plates is studied using molec- ular dynamics simulation. Two grain sizes are considered; deformation in the fine-grained sample is mainly caused by grain-boundary processes (sliding and rotation), while dislocation plasticity dominates in the coarse- grained sample. We show that the sample distortion is reflected by the center-of-mass motion of the grains. Grain rotation is responsible for surface roughening after the loading process. While the plastic deformation is caused by the loading process, grain rearrangements under load release also contribute considerably to the final sample distortion.