Variation Principles Research Articles

Investigating Wind Characteristics and Temporal Variations in the Lower Troposphere over the Northeastern Qinghai–Tibet Plateau Using a Doppler LiDAR

Knowledge of wind field characteristics and variation principles in complex topographical regions is of great importance for the development of numerical prediction models, aviation safety support, and wind energy utilization. However, there has been limited research focused on the lower-tropospheric wind fields in the Qinghai-Tibet Plateau. This paper aims to study the wind characteristics, vertical distributions, and temporal variations in the northeast of the plateau by analyzing a four-year continuous dataset collected from a Doppler wind LiDAR deployed in Xining, Qinghai Province of China. The results indicate that the prevailing horizontal wind direction in the low levels is primarily influenced by the mountain-valley wind circulation. However, as the altitude increases, the prevailing winds are predominantly affected by the westerlies. From a diurnal perspective, noticeable transition processes between up-valley and down-valley winds can be observed. The west-northwest wind (down-valley wind) dominates from late night to morning, while the east-southeast wind (up-valley wind) prevails from afternoon to early evening. The vertical winds in the low levels exhibit a downward motion during the daytime and an upward motion during the nighttime. In this plateau valley, the wind shear exponent is found to be highest in spring and lowest in winter, and it is generally lower during the daytime compared to the nighttime.

Bias in Laboratory Medicine: The Dark Side of the Moon.

Physicians increasingly use laboratory-produced information for disease diagnosis, patient monitoring, treatment planning, and evaluations of treatment effectiveness. Bias is the systematic deviation of laboratory test results from the actual value, which can cause misdiagnosis or misestimation of disease prognosis and increase healthcare costs. Properly estimating and treating bias can help to reduce laboratory errors, improve patient safety, and considerably reduce healthcare costs. A bias that is statistically and medically significant should be eliminated or corrected. In this review, the theoretical aspects of bias based on metrological, statistical, laboratory, and biological variation principles are discussed. These principles are then applied to laboratory and diagnostic medicine for practical use from clinical perspectives.

Correlation-Based Feature Selection to Identify Functional Dynamics in Proteins.

To interpret molecular dynamics simulations of biomolecular systems, systematic dimensionality reduction methods are commonly employed. Among others, this includes principal component analysis (PCA) and time-lagged independent component analysis (TICA), which aim to maximize the variance and the time scale of the first components, respectively. A crucial first step of such an analysis is the identification of suitable and relevant input coordinates (the so-called features), such as backbone dihedral angles and interresidue distances. As typically only a small subset of those coordinates is involved in a specific biomolecular process, it is important to discard the remaining uncorrelated motions or weakly correlated noise coordinates. This is because they may exhibit large amplitudes or long time scales and therefore will be erroneously considered important by PCA and TICA, respectively. To discriminate collective motions underlying functional dynamics from uncorrelated motions, the correlation matrix of the input coordinates is block-diagonalized by a clustering method. This strategy avoids possible bias due to presumed functional observables and conformational states or variation principles that maximize variance or time scales. Considering several linear and nonlinear correlation measures and various clustering algorithms, it is shown that the combination of linear correlation and the Leiden community detection algorithm yields excellent results for all considered model systems. These include the functional motion of T4 lysozyme to demonstrate the successful identification of collective motion, as well as the folding of the villin headpiece to highlight the physical interpretation of the correlated motions in terms of a functional mechanism.

Cylindrical Cavity Optimization for Resonant-Tunneling Diode Oscillators

In this work, the theoretical shapes of cavities were investigated as suited for resonant-tunneling diode (RTD) lumped-element oscillators to achieve the highest possible operational frequency. The scope of this work is restricted to cylindrical cavities that are in their dimensions much smaller or similar to the free-space wavelength. The idea is to find a shape that has the highest quality factor possible. The proposed analysis is based on functional variation principles coupled with electric-field integral equation (EFIE) method of moments solver. Simple design parameters were found covering the cavities that are much smaller than the free-space wavelength. The maximum reachable frequency was calculated with these types of new cavities using some theoretical RTD parameters. The theoretical limitation of frequency was also defined for given RTD parameters and fabrication limitations originating from the contact resistance and RTD radius. In order to demonstrate the significance of the findings, a theoretical geometry was compared with a practical resonator shape.

Analysis of spatiotemporal variations and effects of regional functions in rural China

AbstractThis study analyzes the spatiotemporal evolution and effects of regional functions in rural China and summarizes the spatiotemporal characteristics of rural Chinese regional functions from 2005 to 2015. The results of this study are as follows. (a) The values of the regional functions of rural China generally exhibit a “V‐shaped” distribution such that these values are high in eastern and western China and low in central China, and are high in northern China and low in southern China. (b) The overall functions of rural Chinese regions vary distinctly by region across northeastern China, eastern China, central China, and western China. (c) The spatial variation of regional production function values in rural China also exhibits a gradually declining trend, with the highest values in eastern China, followed by northeastern, central, and western China. This pattern exhibits a relatively strong coupling relationship with the spatial variation principles governing China's natural environment, resource carrying capacity, and economic development level. Overall, regional ecological function values do not exhibit any significant variation, but they do exhibit a gradually declining trend, starting from western and northern China and moving to eastern and southern China. (d) The degree of spatial spillover received by a given region from a neighboring region's production, living, or ecological function is stronger than the effect of the error shock from the corresponding function of the neighboring region. The effects of influencing factors on different regions exhibit significant variation.

Finite Element Analysis and Polarization Test of IDEs Piezoelectric Actuator.

A new type of actuator is presented in the paper that integrates the IDEs into a conventional piezoelectric sheet. The electrodes and polarization play a key role in the strain. Adopting constitutive equations of piezoelectric theory and variation principles in elasticity theory, the piezoelectric component dynamic equation was deduced. Several finite element models of the IDEs piezoelectric actuator were established in ANSYS. The effect of branch electrodes on the strain of the actuator was analyzed. The results show that the strain can be bigger than that of the conventional piezoelectric sheet by decreasing the gap and increasing the width of electrodes. According to the FEM result, some IDEs piezoelectric actuators were prepared. The distribution of the static electric field inside the actuator was researched to determine the polarization voltage. The 2671 high voltage power and DU-20 temperature-controlled oil bath was applied to explore the polarization process. The effect of the voltage, time and temperature on the strain of the actuator was researched by a TF2000 and SIOS laser interferometer. The results show that the optimum polarization is 800 V, for 60 min and at 150 °C. The strain of the IDEs piezoelectric actuator is 1.87 times that of the conventional piezoelectric actuator. The actuators could prove to be helpful applications for micro-nano devices.

Correction of shear lag warping function of steel bottom – Corrugated steel web box girder

To clarify the shear lag effect of the cross-section of steel bottom – corrugated steel web box girder, this study investigated the effect of replacing the concrete floor with a steel bottom on the additional warping displacement of the steel-concrete cross-section based on the energy variation principles of the cosine function method. Two methods are used to derive the maximum shear angle difference function of each member. Firstly, considering the influence of different material modulus and geometric size on the composite section of box girder, the warpage function is modified. On the other hand, the maximum angle difference function of each member on the composite section is assumed, and its expression is derived by using the matrix eigenvalue method. Refer to bridges under construction, a 6 m scale model beam is made and designed as the single box double chamber steel bottom - corrugated steel web box girder. By comparing the General beam theory, finite element method (FEM), Model beam test value and the correction method in this paper, the validity of this theory is verified.

Nonlinear vibration model and response characteristic of drilling risers in deep-sea under soft suspension evacuation condition

In order to provide theoretical reference for the design and operation of soft suspension riser, firstly, a three-dimensional nonlinear vibration model of risers is established using the Hamilton variation and virtual work principles. In the model, three main nonlinear factors were taken into account: longitudinal-lateral (LG/LT) coupling vibration, vortex induced vibration (VIV) and large deformation. The finite element method (FEM) is used to realize the numerical solution of the nonlinear vibration model. Secondly, the correctness and effectiveness of the nonlinear vibration model is verified by the experimental measured data and ANSYS software. The progressiveness of the model is verified by comparing with the uncoupled model and hard suspension, and it demonstrate that, the proposed model can reflect the high nonlinearity of the riser system and describe the nonlinear vibration of the real riser more accurately. The natural frequency of the nonlinear model was much higher and the modal response more complex. The nonlinear coupling effects increase the vibration amplitude in the cross flow (CF) direction and the in-line (IL) direction. Thirdly, the model was used to analyze the effects of structure parameters, environmental parameters and operation parameters on the response characteristics of soft suspension evacuation riser. Some important phenomena have been found: reasonable allocation rate of buoyancy block can effectively restrain the vibration of riser. The optimal allocation rate of buoyancy block is related to the riser structure and operation conditions, which can be determined using proposed nonlinear model. Meanwhile, it is necessary to evacuate along the flow direction as much as possible, with an evacuation speed of lower than 1 m/s.

Buckling Behavior of Thin-Walled Stainless-Steel Lining Wrapped in Water-Supply Pipe under Negative Pressure

This paper presents a study about the buckling behavior of thin stainless-steel lining (SSL) for trenchless repair of urban water supply networks under negative pressure. The critical buckling pressure and displacement (p–δ) curves, temperature changing curves, hoop and axial strain of the lining monitoring section and the strain changes with system pressure (p–ε) of the lining under the action of different diameters, different lining wall thickness and different ventilation modes were obtained through five groups of full-scale tests. The variation principles of the post-buckling pressure and the reduction regularity of the flowing section of the lining were further investigated. By comparing different pipeline buckling models and introducing thin-shell theory, the buckling model of liner supported by existing pipe was established. The comparison between the test results and thin-shell theory indicates that one of the significances of the enhancement coefficient k value is to change the constraint condition of the aspect ratio, l/R, thus increasing the critical buckling pressure of the lining. Finally, an improved lining buckling prediction model (enhancement model) is presented. A previous test is used as a case study with the results showing that the enhanced model is able to predict critical buckling pressure and lobe-starting amount of the liner, which can provide guidance for trenchless restoration of the liner with thin-walled stainless steel.

Quantitative Analysis on Maximum Efficiency Point and Specific High-Efficiency Region of Permanent-Magnet Machines

In this article, the efficiency function of the permanent-magnet (PM) machines is reconstructed by the quantitative loss expressions. Then, the efficiency function is used to quantitatively analyze the maximum efficiency point and the specific high-efficiency region. General principles of improving the maximum efficiency and the regulation of the specific high-efficiency region for PM machines are investigated. First, the loss expressions of PM machines, which vary with the speed and the current, are presented. Moreover, an accurate efficiency function is established to calculate the efficiency map of PM machines quickly. Furthermore, the maximum efficiency point and the specific high-efficiency region of PM machines are derived, as well as their variation principles with loss distributions are studied. Furthermore, a 12-slots 10-poles PM machine and a 48-slots 22-poles PM machine are designed to verify the analytical results. Subsequently, their electromagnetic performances and the efficiency maps are calculated and compared by the finite-element method. Finally, both PM machines are prototyped and experimental results are given for validations.

Precision analysis model and experimentation of vision reconstruction with two cameras and 3D orientation reference

Active vision reconstruction is widely used in industrial manufacturing and three-dimensional inspection. The reconstruction accuracy is an important problem to be investigated for the inspection process. The paper conducts an analysis study of the reconstruction error for the vision reconstruction with a planar laser, two cameras and a 3D orientation board. The variation principles of the spatial coordinates caused by the variations of the extrinsic parameters of the cameras, intrinsic parameters of the internal camera, and image coordinate points of the internal camera, are modeled and analyzed in this paper. The analysis is also proved by the verification experiments, which provides the application potential for other active-vision-based reconstructions.

Prescribed convergence analysis of recurrent neural networks with parameter variations

Recurrent neural networks are designed to be convergent to the desired equilibrium point for their applications. Network parameter variations lead network states to other different points. So this paper discusses the prescribed convergence problem of recurrent neural networks with parameter variations. Firstly, we recurrent neural networks’ equilibrium point variation principles when parameters are changed. Then we design one track controller to make recurrent neural networks be convergent to the prescribed equilibrium for known parameter variations. Next, we present one adaptive controller to lead network states to the desired equilibrium for unknown parameter variations. At last, two examples are given for validating the presented methods.

Critical Analysis of the Equations of Statics in the Bending Theories of Composite Plates Obtained on the Basis of Variational Principles of Elasticity Theory 2. Particular Low-Order Theories

In a geometrically linear formulation based on the use of variation principles of elasticity theory, the twodimensional equations of statics and the boundary conditions at the edge of an orthotropic bending plate are obtained within the framework of the classical theory and two low-order nonclassical theories: Reddy–Nemirovskii and Margueere–Timoshenko–Naghdi ones. It is shown that using the hypotheses of the classical theory, the two-dimensional static equations and the corresponding boundary conditions ensure the equilibrium of an arbitrary subarea of the structure and of the entire plate as a rigid whole; within the framework of the Reddy–Nemirovskii theory, this equilibrium is disturbed in moments and forces in the transverse direction; within the framework of the Margueere–Timoshenko–Naghdi theory, the equilibrium is disturbed in the membrane forces and moments. An example of cylindrical bending of rectangular elongate orthotropic and isotropic plates clamped along one longitudinal edge and loaded in the transverse direction on the other longitudinal edge is considered. It is shown that, within the framework of the classical, Reissner, and Ambartsumyan theories, this problem is statically determinate and the shearing force, according to these theories, is determined elementary by the method of sections. According to the Reddy–Nemirovskii theory, this problem is statically indeterminate and has a rather awkward solution. It is demonstrated that, within the framework of the Reddy–Nemirovskii theory, the shearing force is zero on the clamped edge, i.e., the plate as a whole cannot be in equilibrium. In the vicinity of such an edge, there arises a pronounced false boundary effect, which does not take place in reality, because it is located inside the zone of the boundary layer and cannot be calculated by this theory.

ПРИМЕНЕНИЕ ШАГОВО-ИТЕРАЦИОННОГО МЕТОДА ПРИ РАСЧЕТЕ ИЗГИБАЕМЫХ ПРЕДВАРИТЕЛЬНО НАПРЯЖЕННЫХ СБОРНО-МОНОЛИТНЫХ ЭЛЕМЕНТОВ С УЧЕТОМ ФИЗИЧЕСКОЙ НЕЛИНЕЙНОСТИ

precast and monolithic reinforced concrete structures with and without prestressing armature voltages are used as newly designed independent ones, and are the result of work to strengthen existing structures by increasing the cross section. In both cases, the cross-section of such elements is considered as a two-layer, and the resulting composite element operates under load in conditions distributed between the layers of internal forces, the mechanism and the actual value of the distribution of which depends on the physical and mechanical characteristics, the design scheme and the parameters of the contact interaction of the layers. When calculating and designing prestressed reinforced concrete precast and monolithic elements, the shear seam compliance is usually not taken into account, which complicates the analysis of the actual stress-strain state of the structure and contains a certain undisclosed potential for its rational design. One of the possible directions in solving the problem, taking into account the shift of the contact seam, is the use of variational principles of structural mechanics in the calculation of structures such as composite cross-section rods. In the framework of this work, the questions of practical applicability in the structural analysis of composite reinforced concrete precast-monolithic rod of variation principles of structural mechanics based on the method of V.Z. Vlasov – I.E. Mileykovsky in the form of displacements in combination with the stepwise-iterative method of calculation are considered. The results of numerical calculations by the proposed method are presented, which allows to take into account the specifics of the shear bonds of the precast and monolithic layer, to carry out practical accounting of the seam compliance, as well as to take into account the physical nonlinearity of the characteristics of materials, which allows the rational design of precast monolithic structures.

Study on the Thin Plate Model with Elastic Foundation Boundary of Overlying Strata for Backfill Mining

In order to better study the movement principles of overlying strata during backfill mining, we established a thin plate model on an elastic foundation with elastic foundation boundary of the main roof. And by the finite difference method, the variation principles of the main roof’s principal moments and maximum subsidence ω0 with the elastic foundation coefficient k1 of the coal seam, the elastic foundation coefficient k2 of backfill body, the thickness h, Young’s modulus E, and Poisson’s ratio μ of main roof are calculated and studied. Using these calculations, we were able to determine that the main roof had three principal bending moment extreme points, including Mzz in backfill areas, Mc of the long side area, and Md of the short side area. The distance Lc of Mc advancing coal wall continuously increased with the increase in k2, while the principal moment of main roof’s middle area decreased with an increase in k2; when k2 became larger, the maximum principal moment in the midpoint of main roof transferred to the surrounding and the maximum principal moments was in four-corner area; Mc and Md decreased with an increase in k2, and Md was more sensitive to k2 than Mc; and Md decreased significantly with the increase in k2. Lc continuously decreased with the increase in k1, while Mc, Md and Mzz increased with the increase in k1 and the reduced amplitude of Mzz was the minimum. The effect of μ on principal bending moments and ω0 was very small; The growth rate of Mzz was the largest when E or h increased. Md, Mzz, and Lc remained unchanged when k1, k2, and Young’s modulus E of the main roof increased while the ratio value remained constant (k1/k2/E). Finally, the theoretical calculations were applied to the I26 backfill working face in the Xingdong mine to calculate the final subsidence amounts of the main roof. Field observations and theoretical calculations were about 48 mm, verifying the method’s applicability.

Construction of the bending model of micropolar elastic thin beams with a circular axis and its implementation using finite element method

This paper considers the problem of transition from the system of two-dimensional equations of the micropolar (moment) theory of elasticity in a thin curved area to the one-dimensional system of equations describing deformation of the micropolar elastic thin beam with a circular axis. During the transition process, Timoshenko's hypotheses generalized to the micropolar case are applied. As a result, the applied model (with independent fields of displacements and rotation) of a micropolar elastic thin beam with a circular axis has been constructed. It is shown that the model includes the law of conservation of energy, energy theorems and variation principles. All main functionals for the model of the micropolar elastic thin beam with a circular axis are obtained from the functional of the two-dimensional micropolar theory of elasticity, containing only the first derivatives of displacements and rotations. The finite element method (FEM) is taken to study the boundary problems of statics and dynamics of applied model of the micropolar elastic thin beam with a circular axis. The basic concepts and stages of the FEM are formulated: the discretization, the selection of basic nodal unknowns, the approximation of the solution, and the construction of the basic FEM equations. The finite-element solutions of some problems of statics and problems on natural vibrations of beams with a circular axis are considered according to the micropolar theory of elasticity. A comparative analysis with similar problems of beams with a circular axis according to the classical theory of elasticity is carried out. Based on the results, some effective properties of beams with a circular axis have been established when considering their deformations in the context of the micropolar theory of elasticity.

МЕТОДИЧНЕ ОБҐРУНТУВАННЯ ВАРІАЦІЙНОГО ПРИНЦИПУ ГАМІЛЬТОНА-ОСТРОГРАДСЬКОГО

It is stated on the basis of the current research analysis that the foundation of the bases of analytical methods of research of physical systems and variation methods have remained outside the attention of methodological science and, therefore, coverage of methodological aspects of foundation the topic “Variation integral principle of stationary action” in teaching theoretical physics in pedagogical universities is relevant.Based on the fact that the mechanical state at each moment is clearly defined as a configuration system as well as velocities system, we introduce some arbitrary dynamic function of the system state that is connected to the coordinates and velocities of all material points and perhaps time. The value of this function at each point in time, we multiply by dt and integrate for a period of time : If we distract from the action of specified forces, and consider only the effect of superimposed ties, it is clear that without breaking the connection with the bodies which limit the movement of material points, the system from position 1 to position 2 during the same period of time could move a large number of close routes, which are not described by equations of motion, and answer only to the linkage equation. To set the criterion that distinguishes the real (direct) path of the system from all other kinematically possible (virtual) for given links, we determine the variation of the resulting integral and come to the conclusion that the actual motion of the mechanical system between two given positions q(t1) and q(t2) configuration space occurs along the trajectory for which the action functional S(q, t1, t2) acquires a stationary value, and, in addition, we obtain the Lagrange equation which, like Newton’s second law, is equations of motion. To consolidate the material, students are invited to consider the problem of the movement of the harmonic oscillator and determine the magnitude of the action between two points along the trajectory and along another close line between the same points. This technique allows students to form a sufficiently deep and stable understanding of this principle and gives an idea of the use of this principle to solve problems of mechanics, which are difficult to solve using only Newton’s laws. Key words: methods of teaching physics, variation principles, Lagrange equations, integral of action, future teachers of physics.

Analysis of Prestressed Bent Precast-Cast-<i>In-Situ</i> Structures in Vlasov-Mileykovsky Method with Physical Non-Linearity of Material

Precast reinforced concrete structures with and without reinforcement pre-stressing are used both as newly designed independent ones and are the result of work to strengthen the existing structures by increasing the section. In both cases, the cross section of such elements is considered as a two-layer section, and the resulting composite element works under load under conditions distributed between the layers of internal forces, the mechanism and actual distribution of which depends on the physical and mechanical characteristics, the design scheme and the layers contact interaction parameters. When calculating and designing prestressed reinforced concrete precast-monolithic elements, the shear seam ductility is usually not paid much attention to, which complicates the structure actual stress-strain state analysis and contains a certain undiscovered potential of its rational design. One of the possible directions in solving the problem, which takes into account the contact seam shift, is the structural mechanics variation principles use in the calculation of structures such as rods of composite section. The questions of a composite reinforced concrete precast-monolithic rod of the variation principles of structural mechanics based on the method of V.Z. Vlasov - I.E. Mileykovsky in the displacements form in combination with the step-iterative method of calculation practical applicability in the structural analysis is considered in this work,. The numerical calculations results according to the proposed method are given. This allows to take into account the precast and monolithic layers shear connections specifics, to take practical account of weld compliance, and also to take into account the material characteristics’ physical non-linearity, which contributes to the precast monolithic structures rational design.

Variation Formulations of Inverse Problems in Forecasting the Residual Life of Composites

An approach is proposed on the basis of more precise formulations of the forecasting problem and developed within the framework of variation principles for the solution of inverse problems, into which precise estimation of forecast solutions is incorporated for the first time, thus providing the possibility to obtain new scientifically substantiated results and achieve a required precision of forecasting. An original model is constructed to forecast the residual life and longevity of composites and describe the processes occurring in polymer composite materials and structures under the simultaneous influence of several destabilizing physical factors at the physical level. The application of a newly formulated principle of multiplicity for forecasting models and the first constructed multiparametric models of optimal complexity within the refined variation formulation of inverse forecasting problems of the residual life has appreciably improved the precision of solution for inverse forecasting problems and enhanced the time interval within which the time dependence of the residual life and longevity of composites can be predicted at a specified maximum permissible precision of forecasting. The proposed approach can be used to solve a broad range of problems of forecasting the residual life, longevity, and strength of composites.

The estimation of the internal dimensions of the channel for transport of atoms, molecules from the variation principles and the conditions of its local symmetry

Properties of channel in order to transport atoms (ions, molecules) is considered from point of its symmetry. Lagrange function of the transport channel is constructed. Properties of the Lagrange function and types of symmetry of the channel allow to estimate its inner size. Crystallographic channel of quartz and its dislocations are used as particular example.